S3.1 The periodic table: Classification of elements - IB Chemistry Question Bank

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S3.1 The periodic table: Classification of elements

Practice exam-style IB Chemistry questions for The periodic table: Classification of elements, aligned with the syllabus and grouped by topic.

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Question 1

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SL • Paper 1A

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The p-block of the periodic table is represented by the shaded region in diagram

A.

B.

C.

D. Question 2

SL • Paper 1A

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SL • Paper 1A

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The oxide in period 3 that is amphoteric is

A.

$Al_2O_3$

B.

$MgO$

C.

$Na_2O$

D.

$SO_3$

Question 3

SL • Paper 1A

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SL • Paper 1A

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An atom has the electron configuration $[Ne]\ 3s^2\ 3p^5$ .

The period, group and classification of the element are

A.

period 5, group 17, noble gas

B.

period 3, group 15, halogen

C.

period 3, group 17, halogen

D.

period 3, group 18, noble gas

Question 4

SL • Paper 1A

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SL • Paper 1A

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Chlorine water is added to aqueous potassium iodide.

The equation for the reaction is

A.

$Cl_2(aq) + 2K^+(aq) \to 2KCl(aq)$

B.

$I_2(aq) + 2Cl^-(aq) \to 2I^-(aq) + Cl_2(aq)$

C.

$Cl_2(aq) + 2I^-(aq) \to 2Cl^-(aq) + I_2(aq)$

D.

$2Cl^-(aq) + I_2(aq) \to Cl_2(aq) + 2I^-(aq)$

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Question 5

SL • Paper 1A

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SL • Paper 1A

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The oxidation state of hydrogen in $CaH_2$ is

A.

$-1$

B.

$+1$

C.

$+2$

D.

$0$

Question 6

HL • Paper 1A

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HL • Paper 1A

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The electron configuration of $Cu^{2+}$ is

A.

$[Ar]\ 4s^1\ 3d^8$

B.

$[Ar]\ 4s^2\ 3d^7$

C.

$[Ar]\ 3d^8$

D.

$[Ar]\ 3d^9$

Question 7

HL • Paper 1A

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HL • Paper 1A

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A transition metal complex absorbs orange light.

The colour most likely observed is

A.

green

B.

orange

C.

red

D.

blue

Question 8

SL • Paper 2

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SL • Paper 2

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A simplified periodic table is shown with three labelled positions, X, Y and Z.

State the name given to a horizontal row in the periodic table.

[1]

State the classification of element X and the number of valence electrons in an atom of X.

[2]

State the classification of element Y as metal, non-metal or metalloid.

[1]

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Question 9

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SL • Paper 1A

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The species $O^{2-}$ , $F^-$ , $Na^+$ and $Mg^{2+}$ are isoelectronic.

The correct order of ionic radius, from largest to smallest, is

A.

$F^- > O^{2-} > Na^+ > Mg^{2+}$

B.

$Mg^{2+} > Na^+ > F^- > O^{2-}$

C.

$O^{2-} > Na^+ > F^- > Mg^{2+}$

D.

$O^{2-} > F^- > Na^+ > Mg^{2+}$

Question 10

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HL • Paper 1A

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The first ionization energy of aluminium is lower than that of magnesium.

The best explanation is that the electron removed from aluminium is

A.

paired in a $3p$ orbital, causing electron-electron repulsion

B.

closer to the nucleus because aluminium has a greater nuclear charge

C.

a $3s$ electron, which is more strongly shielded than a $3p$ electron

D.

a $3p$ electron, which is higher in energy than a $3s$ electron

Question 11

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HL • Paper 1A

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A transition element is an element that has an incomplete d sublevel in its atoms or forms at least one stable ion with an incomplete d sublevel.

The diagram that represents a transition element is

A.

B.

C.

D. Question 12

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HL • Paper 1A

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A coloured complex absorbs light of wavelength $600\ \text{nm}$ .

Using $c = \lambda f$ and $c = 3.00 \times 10^8\ \text{m s}^{-1}$ , the frequency of the absorbed light is

A.

$1.80 \times 10^{11}\ \text{s}^{-1}$

B.

$5.00 \times 10^{14}\ \text{s}^{-1}$

C.

$5.00 \times 10^5\ \text{s}^{-1}$

D.

$2.00 \times 10^{-15}\ \text{s}^{-1}$

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Question 13

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SL • Paper 2

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An atom of element E has the electron configuration $[Ar]4s^23d^{10}4p^4$ .

Deduce the period and group number of element E.

[2]

Deduce the number of valence electrons and the block of the periodic table to which element E belongs.

[2]

Question 14

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SL • Paper 2

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The graph shows periodic trends for selected period 3 elements.

Element	Atomic radius / pm	Electronegativity (Pauling)
Na	186	0.93
Mg	160	1.31
Al	143	1.61
Si	118	1.90
P	110	2.19
S	104	2.58
Cl	99	3.16

Describe the trend in atomic radius across period 3 from sodium to chlorine.

[1]

Explain the trend in atomic radius across period 3.

[2]

State the general trend in electronegativity across period 3 from left to right.

[1]

Question 15

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SL • Paper 2

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Group 1 metals react with water, and group 17 elements react with halide ions according to their reactivity trends.

Write the balanced equation for the reaction of potassium with water.

[2]

Explain why chlorine displaces iodide ions from aqueous potassium iodide, but iodine does not displace chloride ions from aqueous potassium chloride.

[2]

Question 16

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SL • Paper 2

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Oxides of elements show a change in acid-base character across a period.

Write the equation for the reaction of sodium oxide with water.

[1]

Write the equation for the reaction of sulfur trioxide with water.

[1]

Outline how the acid-base character of the oxides changes across period 3 from sodium to sulfur.

[2]

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Question 17

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The table gives information about four elements labelled A to D. The letters are not chemical symbols.

Element	Electron configuration
A	$[\text{Ne}]\,3s^1$
B	$[\text{Ne}]\,3s^2\,3p^4$
C	$[\text{Ar}]\,3d^6\,4s^2$
D	$[\text{Ne}]\,3s^2\,3p^2$

Deduce the period and group of element B from its electron configuration.

[2]

Identify the block and broad classification of element C.

[1]

Suggest why element D is classified as a metalloid rather than simply as a metal or non-metal.

[1]

Question 18

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SL • Paper 1B

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A simulation compares the reactions of three group 1 metals with excess water under the same conditions.

Group 1 metal	Time for reaction to finish / s	Temperature increase / $^\circ\text{C}$
Lithium	75	4
Sodium	30	8
Potassium	12	13

State the gas produced in the reactions.

[1]

Describe how the reactivity changes from lithium to potassium using the data.

[1]

Explain the change in reactivity down group 1.

[2]

Question 19

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HL • Paper 1A

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Transition elements commonly show variable oxidation states.

The best explanation is that

A.

their filled p sublevels can expand into d sublevels

B.

their atoms have the same first ionization energy across the period

C.

their inner-shell electrons are removed before valence electrons

D.

their $4s$ and $3d$ electrons are relatively close in energy

Question 20

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SL • Paper 2

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Oxidation states can be deduced using the usual rules and the overall charge of the species.

Deduce the oxidation state of hydrogen in $CaH_2$ and oxygen in $Na_2O_2$ .

[2]

Deduce the oxidation state of sulfur in $SO_4^{2-}$ and give the systematic name of this oxyanion using a Roman numeral.

[2]

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Question 21

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The graph shows first ionization energies for the elements in period 2.

State the general trend in first ionization energy across period 2.

[1]

Explain why the first ionization energy of boron is lower than that of beryllium.

[2]

Explain why the first ionization energy of oxygen is lower than that of nitrogen.

[1]

Question 22

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HL • Paper 2

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Zinc and scandium are both found in the first row of the d-block, but their classification as transition elements is considered differently.

Define the term transition element.

[1]

Explain why zinc is not usually classified as a transition element.

[2]

State one characteristic property commonly shown by transition elements that is linked to incomplete d-sublevels.

[1]

Question 23

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HL • Paper 2

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Chromium and iron are first-row transition elements.

State the condensed electron configuration of a chromium atom.

[1]

Deduce the electron configuration of $Cr^{3+}$ .

[1]

Deduce the electron configuration of $Fe^{2+}$ , given that $Fe$ is $[Ar]4s^23d^6$ .

[1]

State which sublevel loses electrons first when first-row transition metal atoms form ions.

[1]

Question 24

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HL • Paper 2

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An aqueous transition metal complex absorbs light of wavelength $610\ \text{nm}$ . Use $c=\lambda f$ and $c=3.00\times 10^8\ \text{m s}^{-1}$ .

Calculate the frequency of the light absorbed.

[2]

Deduce the colour observed if the absorbed light is orange-red.

[1]

State one factor that can affect the colour of a transition metal complex.

[1]

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Question 25

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SL • Paper 1B

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The graph shows first ionization energy, atomic radius and electronegativity for selected period 3 elements.

Element	First ionization energy / kJ mol $^{-1}$	Atomic radius / pm	Electronegativity / Pauling scale
Sodium (Na)	496	186	0.93
Magnesium (Mg)	738	160	1.31
Aluminium (Al)	578	143	1.61
Silicon (Si)	787	118	1.90
Phosphorus (P)	1012	110	2.19
Sulfur (S)	1000	104	2.58
Chlorine (Cl)	1251	99	3.16

Describe the trend in atomic radius across the period shown.

[1]

Explain the trend in atomic radius across the period.

[2]

Use the data to suggest the element in the graph with the strongest attraction for bonding electrons, giving a reason.

[2]

Question 26

SL • Paper 1B

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SL • Paper 1B

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Aqueous halogens were added separately to aqueous solutions containing halide ions. The observations after mixing and shaking are shown.

Halogen added	$Cl^-(aq)$	$Br^-(aq)$	$I^-(aq)$
$Cl_2$ (aq)	no visible change	solution turns orange-brown	solution turns brown
$Br_2$ (aq)	no visible change	no visible change	solution turns brown
$I_2$ (aq)	no visible change	no visible change	no visible change

Identify one mixture in which a displacement reaction occurs.

[1]

Write the ionic equation for the reaction between chlorine and bromide ions.

[2]

Use the observations to deduce the order of decreasing reactivity of the three halogens.

[1]

Question 27

SL • Paper 1B

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SL • Paper 1B

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The table shows formulae of some compounds and ions containing hydrogen or oxygen. Some oxidation states are missing.

Species / formula	Given oxidation state(s)	Missing oxidation state
$\text{NaH}$	Na = $+1$	H = ?
$\text{H}_2\text{O}_2$	H = $+1$	O = ?
$\text{NO}_3^-$	O = $-2$	N = ?
$\text{Cl}_2$	—	Cl = ?

Deduce the oxidation state of hydrogen in sodium hydride, $NaH$ .

[1]

Deduce the oxidation state of oxygen in hydrogen peroxide, $H_2O_2$ .

[1]

Deduce the oxidation state of nitrogen in $NO_3^-$ .

[1]

Explain why chlorine has oxidation state zero in $Cl_2$ .

[1]

Question 28

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HL • Paper 1B

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The table compares selected period 4 d-block elements and some of their common ions.

Element	Atom electron configuration	Common ion(s) / electron configuration
Sc	$[Ar] 4s^2 3d^1$	$\text{Sc}^{2+} = [Ar] 3d^1$ ; $\text{Sc}^{3+} = [Ar]$
Ti	$[Ar] 4s^2 3d^2$	$\text{Ti}^{2+} = [Ar] 3d^2$
V	$[Ar] 4s^2 3d^3$	$\text{V}^{2+} = [Ar] 3d^3$
Fe	$[Ar] 4s^2 3d^6$	$\text{Fe}^{2+} = [Ar] 3d^6$
Cu	$[Ar] 4s^1 3d^{10}$	$\text{Cu}^{2+} = [Ar] 3d^9$
Zn	$[Ar] 4s^2 3d^{10}$	$\text{Zn}^{2+} = [Ar] 3d^{10}$

Using the data, identify the element that is d-block but is not normally classified as a transition element.

[1]

Explain the identification in part (a) using electron configurations.

[2]

Evaluate one argument for including scandium as a transition element, based on the data.

[1]

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Question 29

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A table compares successive ionization energies for calcium and vanadium after the argon core.

Ionization energy	Ca / kJ mol $^{-1}$	V / kJ mol $^{-1}$
1st	590	650
2nd	1145	1414
3rd	4912	2830
4th	6491	4564
5th	8153	6290

State what is meant by successive ionization energies.

[1]

Explain why vanadium can form several oxidation states.

[2]

Deduce the electron configuration of $V^{3+}$ , given that $V$ is $[Ar]4s^23d^3$ .

[1]

Question 30

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HL • Paper 2

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A student uses colorimetry to determine the concentration of a coloured transition metal complex in solution.

Outline how the calibration graph is used to determine the concentration of the unknown solution.

[2]

Explain why a wavelength strongly absorbed by the complex is chosen for the colorimeter.

[2]

Question 31

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SL • Paper 1B

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Several period 3 oxides were added separately to water. Universal indicator and pH data were recorded after stirring.

Oxide	Indicator colour	pH
$Na_2O$	purple	13
$MgO$	blue	10
$Al_2O_3$	green	7
$P_4O_{10}$	red	2
$SO_2$	red	2

Classify sodium oxide and sulfur dioxide as basic, acidic or amphoteric oxides.

[2]

Write an equation for the reaction of sodium oxide with water.

[1]

Explain why the data support the idea that metallic and non-metallic properties form a continuum across period 3.

[2]

Question 32

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HL • Paper 1B

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The graph shows the first ionization energies of period 2 elements from lithium to neon.

Describe the overall trend in first ionization energy across period 2.

[1]

Explain the discontinuity between beryllium and boron.

[2]

Explain the discontinuity between nitrogen and oxygen.

[2]

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Question 33

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A transition metal complex appears blue-green in aqueous solution. A colour wheel and absorption spectrum for the solution are shown. Use $c = \lambda f$ and $c = 3.00 \times 10^8\ \text{m s}^{-1}$ .

State the colour of light mainly absorbed by the complex.

[1]

Determine the wavelength at maximum absorbance from the spectrum, in metres.

[1]

Calculate the frequency of light at maximum absorbance.

[2]

Explain why absorption of this light gives rise to the observed colour.

[1]

Question 34

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HL • Paper 1B

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The table gives neutral atom electron configurations for chromium, iron and copper, and lists some ions formed by these elements.

Species	Electron configuration
$\text{Cr}$	$[\text{Ar}]4s^1\ 3d^5$
$\text{Cr}^{2+}$	$[\text{Ar}]3d^4$
$\text{Fe}$	$[\text{Ar}]4s^2\ 3d^6$
$\text{Fe}^{2+}$	$[\text{Ar}]3d^6$
$\text{Cu}$	$[\text{Ar}]4s^1\ 3d^{10}$
$\text{Cu}^{+}$	$[\text{Ar}]3d^{10}$
$\text{Zn}^{2+}$	$[\text{Ar}]3d^{10}$

Deduce the electron configuration of $Fe^{3+}$ from $Fe: [Ar]4s^2 3d^6$ .

[1]

Deduce the electron configuration of $Cu^{2+}$ from $Cu: [Ar]4s^1 3d^{10}$ .

[1]

Outline the rule used to decide which electrons are removed first when first-row transition metal ions form.

[1]

Using the data, suggest why copper(II) compounds are more likely to be coloured than zinc(II) compounds.

[1]

Question 35

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SL • Paper 2

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The electron configurations of three neutral atoms are shown.

A: $[\text{Ne}]\ 3s^2\ 3p^5$

B: $[\text{Ar}]\ 4s^2$

C: $[\text{Ar}]\ 4s^2\ 3d^{10}\ 4p^3$

Consider element A.

I.

Deduce the period, group and block of element A.

[3]

II.

Explain why element A and bromine have similar chemical properties.

[2]

Compare the classifications of elements B and C as metal, metalloid or non-metal, using their positions in the periodic table.

[2]

Hydrogen is often placed above group 1. Suggest why this placement does not make hydrogen an alkali metal.

[1]

Question 36

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SL • Paper 2

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The figure shows selected periodic trends for elements in period 3 and group 17.

Species	Series	Atomic radius / pm	Electronegativity / Pauling	Ionic radius / pm
Na	Period 3	186	0.9	—
Mg	Period 3	160	1.3	—
Al	Period 3	143	1.6	—
Si	Period 3	118	1.9	—
P	Period 3	110	2.2	—
S	Period 3	104	2.6	—
Cl	Period 3	99	3.2	—
F	Group 17	64	4.0	—
Cl	Group 17	99	3.2	—
Br	Group 17	114	3.0	—
I	Group 17	133	2.7	—
Mg $^{2+}$	Ion	—	—	72

Consider the elements from sodium to chlorine in period 3.

I.

Describe the trends in atomic radius and electronegativity across this part of period 3.

[2]

II.

Explain the trend in atomic radius across period 3.

[2]

Consider the halogens fluorine, chlorine, bromine and iodine.

I.

State the trend in atomic radius down group 17.

[1]

II.

Explain why electronegativity and non-metallic character decrease down group 17.

[2]

Magnesium commonly forms $Mg^{2+}$ . Suggest why the ionic radius of $Mg^{2+}$ is smaller than the atomic radius of Mg.

[1]

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Question 37

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SL • Paper 2

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Oxidation states are assigned by treating bonds as if they were fully ionic. The species $Na_2O_2$ , $CaH_2$ , $NO_3^-$ , $NO_2^-$ and $Cl_2$ are considered.

Deduce oxidation states in compounds and ions.

I.

Deduce the oxidation state of oxygen in $Na_2O_2$ and hydrogen in $CaH_2$ .

[2]

II.

Deduce the oxidation state of nitrogen in $NO_3^-$ and $NO_2^-$ , and give the systematic names using Roman numerals.

[3]

Explain why the oxidation state of chlorine in $Cl_2$ is zero.

[2]

Question 38

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SL • Paper 2

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An element X was predicted before it was isolated. A modern description of X is that its neutral atom has the electron configuration $[\text{Ar}]\ 4s^2\ 3d^{10}\ 4p^2$ .

Use the electron configuration of X.

I.

Deduce the period, group and block of X.

[3]

II.

Deduce the likely identity of X and classify it as a metal, metalloid or non-metal.

[2]

Discuss how the organization of the periodic table can help chemists predict properties of undiscovered elements.

[2]

Question 39

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HL • Paper 1B

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Successive ionization energies are shown for two period 4 elements, X and Y. Element X forms several stable compounds with different oxidation states, whereas element Y mainly forms compounds in one oxidation state.

State what is meant by successive ionization energies.

[1]

Use the data to identify which element, X or Y, is more likely to be a transition element.

[1]

Explain how the successive ionization energy data account for variable oxidation states in X.

[2]

Deduce the electron configuration of $V^{3+}$ from the neutral atom configuration $V: [Ar]4s^2 3d^3$ .

[1]

Question 40

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HL • Paper 1B

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A student used colorimetry to determine the concentration of a coloured transition metal ion in an unknown solution. Standard solutions were prepared and their absorbance was measured at a selected wavelength.

Use the calibration graph to determine the concentration of the unknown solution.

[1]

Explain why the wavelength selected should be close to the wavelength of maximum absorbance.

[2]

Suggest one source of systematic error in this colorimetric method.

[1]

The ligand around the metal ion is changed and the absorption maximum shifts to a shorter wavelength. Explain what this indicates about the split d-sublevels.

[1]

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Question 41

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SL • Paper 2

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A class compares the reactions of group 1 metals with water and the displacement reactions of halogens with halide ions. Some observations are obtained from teacher demonstrations and some from simulations.

Reaction system	Observation
$\text{Lithium}(s) + \text{water}(l)$	gentle effervescence; moves slowly on the surface
$\text{Sodium}(s) + \text{water}(l)$	vigorous effervescence; metal melts into a ball and moves rapidly
$\text{Potassium}(s) + \text{water}(l)$	very vigorous effervescence; lilac flame observed
$\text{Bromine}(aq) + \text{chloride ions}(aq)$	no visible change; orange colour remains
$\text{Bromine}(aq) + \text{bromide ions}(aq)$	no visible change; orange colour remains
$\text{Bromine}(aq) + \text{iodide ions}(aq)$	orange solution turns brown

Potassium is added to water.

I.

Write a balanced equation for potassium reacting with water, including state symbols.

[2]

II.

Explain why the reactions of group 1 metals with water become more vigorous down the group.

[2]

Deduce whether aqueous bromine reacts with aqueous iodide ions and write the ionic equation if a reaction occurs.

[2]

Evaluate the use of simulations rather than direct practical work for these reactivity comparisons.

[2]

Question 42

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SL • Paper 2

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Oxides across a period show a change from basic metal oxides through amphoteric oxides to acidic non-metal oxides. The oxides $Na_2O$ , $MgO$ , $Al_2O_3$ and $SO_3$ are considered.

Consider the reactions of oxides with water.

I.

Deduce equations for the reactions of $Na_2O$ and $SO_3$ with water.

[2]

II.

Predict whether each solution formed in (a)(i) is acidic or alkaline, giving a reason.

[2]

Explain, in terms of bonding, why metal oxides tend to be basic while non-metal oxides tend to be acidic.

[2]

Discuss how the behaviour of $Al_2O_3$ supports the idea that metallic and non-metallic properties form a continuum.

[2]

Question 43

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HL • Paper 2

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The graph shows first ionization energies for the period 2 elements from lithium to neon.

Consider the general pattern across period 2.

I.

Describe the overall trend in first ionization energy from lithium to neon.

[1]

II.

Explain the general increase in first ionization energy across period 2.

[2]

Consider the two discontinuities in the graph.

I.

Explain why the first ionization energy of boron is lower than that of beryllium.

[2]

II.

Explain why the first ionization energy of oxygen is lower than that of nitrogen. Do not base your answer on the phrase special stability of a half-filled sublevel.

[2]

Discuss how these discontinuities provide evidence for the existence of energy sublevels.

[1]

Question 44

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HL • Paper 2

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Scandium, iron and zinc are d-block elements in period 4. Their common species include $Sc^{3+}$ , $Fe^{2+}$ , $Fe^{3+}$ and $Zn^{2+}$ .

Consider the classification of transition elements.

I.

State the definition of a transition element used in this course.

[1]

II.

Explain why zinc is not classified as a transition element.

[2]

III.

Evaluate one argument for and one argument against including scandium as a transition element.

[2]

Explain how incomplete d sublevels account for three characteristic properties of transition element compounds.

[3]

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Question 45

HL • Paper 2

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HL • Paper 2

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The first-row transition elements form ions by losing electrons from the $4s$ sublevel before the $3d$ sublevel. A graph comparing successive ionization energies for vanadium and calcium is shown.

Deduce electron configurations of vanadium and copper ions.

I.

Deduce the electron configuration of $V^{3+}$ from the neutral atom.

[2]

II.

Deduce the electron configurations of $Cu^+$ and $Cu^{2+}$ .

[2]

III.

Explain why $V^{5+}$ has the electron configuration $[\text{Ar}]$ .

[1]

Explain why variable oxidation states are common among transition elements.

[2]

Using the graph, suggest why $V^{5+}$ is plausible but $Ca^{5+}$ is not.

[1]

Question 46

HL • Paper 2

Hard

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HL • Paper 2

Hard

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A transition metal complex appears blue-green in aqueous solution. It absorbs visible light of wavelength $6.10 \times 10^{-7}\ \text{m}$ . Use $c = 3.00 \times 10^8\ \text{m s}^{-1}$ .

Consider the origin of the colour.

I.

Explain why many transition metal complexes are coloured.

[3]

II.

Calculate the frequency of the absorbed light.

[2]

The ligand is changed to one that causes a larger d-orbital splitting.

I.

If the $d$ -orbital splitting increases, predict the effect on the wavelength and frequency of the light absorbed.

[2]

II.

State one factor, other than ligand identity, that can affect the colour of a transition metal complex.

[1]

Question 47

HL • Paper 2

Hard

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HL • Paper 2

Hard

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A student determines the concentration of a blue solution containing a transition metal complex using colorimetry. A calibration curve of absorbance against concentration is prepared from standard solutions.

Consider the design of the colorimetry method.

I.

Explain why a wavelength near the absorption maximum should be selected.

[2]

II.

Outline how the calibration curve is prepared.

[2]

The absorbance of a diluted sample corresponds on the calibration curve to $1.60 \times 10^{-3}\ \text{mol dm}^{-3}$ . The original sample was diluted by transferring $10.0\ \text{cm}^3$ into a $100.0\ \text{cm}^3$ volumetric flask and making up to the mark. Calculate the concentration of the original sample.

[2]

Evaluate two ways to improve or check the reliability of the colorimetry result.

[2]

Question 48

HL • Paper 2

Hard

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HL • Paper 2

Hard

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The ions $Fe^{2+}$ , $Fe^{3+}$ and $Zn^{2+}$ are compared. Iron is also used as a heterogeneous catalyst in some industrial reactions.

Consider the electron configurations and magnetic behaviour of the ions.

I.

Deduce the electron configurations of $Fe^{2+}$ and $Fe^{3+}$ .

[2]

II.

Explain why compounds containing iron ions may show magnetic properties whereas compounds containing $Zn^{2+}$ often do not.

[2]

Discuss why iron can show both catalytic behaviour and variable oxidation states.

[3]

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S2.4 From models to materials

S3.2 Functional groups

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