Question 4.1
Silver has a full 4d shell in its ground state. Why is it considered a transition element?
Steps only
Ag²⁺ is [Kr]4d⁹, so it has an incomplete d subshell.
Answer
Ag is a transition element.
CLASS 12 · CHEMISTRY · CHAPTER 4
The d-and f-Block Elements
Easy answers to all ten in-text questions and thirty-eight exercises on transition and inner-transition elements.
48 worked answersComplete chapter answers
48 worked answers · short steps first, explanations when you need them
In-text Questions
Textbook pages 92–114
Question 4.2
Why does zinc have the lowest enthalpy of atomisation in the first transition series?
Steps only
Zn's filled 3d¹⁰ shell contributes little to metallic bonding.
Answer
Zn has the lowest atomisation enthalpy.
Question 4.3
Which 3d transition metal shows the largest number of oxidation states, and why?
Steps only
Mn has several available 3d and 4s electrons.
Answer
Manganese; +2 to +7.
Question 4.4
Why is E°(Cu²⁺/Cu) positive (+0.34 V)?
Steps only
High atomisation and ionisation energies are not compensated by hydration.
Answer
Hence E°(Cu²⁺/Cu) is positive.
Question 4.5
Why do first and second ionisation enthalpies vary irregularly across the first transition series?
Steps only
Closely spaced 3d/4s levels and stable d⁵ or d¹⁰ configurations cause irregularities.
Answer
Ionisation enthalpies vary irregularly.
Question 4.6
Why do metals show their highest oxidation states mainly in oxides or fluorides?
Steps only
O and F strongly stabilise highly oxidised metal ions.
Answer
Because O and F are small and highly electronegative.
Question 4.7
Which is the stronger reducing agent, Cr²⁺ or Fe²⁺? Give a reason.
Steps only
Cr²⁺ readily loses an electron to form stable Cr³⁺ (d³).
Answer
Cr²⁺.
Question 4.8
Find the spin-only magnetic moment of aqueous M²⁺ when Z=27.
Steps only
Co²⁺ is d⁷ with 3 unpaired electrons; μ=√(3×5)=3.87 BM.
Answer
3.87 BM.
Question 4.9
Why is Cu⁺ unstable in aqueous solution?
Steps only
2Cu⁺(aq) → Cu²⁺(aq)+Cu(s).
Answer
Cu⁺ disproportionates in water.
Question 4.10
Why is contraction from one actinoid to the next greater than in the lanthanoids?
Steps only
Poor shielding by 5f electrons makes the contraction larger.
Answer
Actinoid contraction is greater.
Chapter 4 Exercises
Textbook pages 115–117
Question 4.1
Write the configurations of Cr³⁺, Pm³⁺, Cu⁺, Ce⁴⁺, Co²⁺, Lu²⁺, Mn²⁺ and Th⁴⁺.
Steps only
Remove outer s electrons first; the listed ions have the configurations shown.
Answer
Cr³⁺ [Ar]3d³; Pm³⁺ [Xe]4f⁴; Cu⁺ [Ar]3d¹⁰; Ce⁴⁺ [Xe]; Co²⁺ [Ar]3d⁷; Lu²⁺ [Xe]4f¹⁴; Mn²⁺ [Ar]3d⁵; Th⁴⁺ [Rn].
Question 4.2
Why are Mn²⁺ compounds more stable than Fe²⁺ compounds towards oxidation to +3?
Steps only
Mn²⁺ is already d⁵; Fe²⁺ forms stable d⁵ Fe³⁺ when oxidised.
Answer
Mn²⁺ is more resistant to oxidation.
Question 4.3
Why does the +2 state become more stable across the first half of the 3d series?
Steps only
The third ionisation energy generally rises across the row.
Answer
The +2 state becomes more stable.
Question 4.4
How much do electronic configurations determine oxidation-state stability in the first transition series? Give examples.
Steps only
Stable d⁵ (Mn²⁺, Fe³⁺) and d¹⁰ (Zn²⁺) states are favoured, along with other energy effects.
Answer
Configurations are important but not the only factor.
Question 4.5
Suggest stable oxidation states for atoms with d³, d⁵, d⁸ and d⁴ configurations.
Steps only
Commonly favourable arrangements include d⁰, d⁵ and d¹⁰; actual stability depends on the element.
Answer
d³→+3; d⁵→+2; d⁸→often +2; d⁴→often +2 or +3.
Question 4.6
Name first-series oxometal anions where the metal oxidation state equals its group number.
Steps only
Vanadate, chromate/dichromate and permanganate contain V(V), Cr(VI) and Mn(VII).
Answer
VO₄³⁻, CrO₄²⁻/Cr₂O₇²⁻ and MnO₄⁻.
Question 4.7
What is lanthanoid contraction, and what are its consequences?
Steps only
Poor 4f shielding causes the La-to-Lu size decrease; Zr and Hf become nearly equal in size.
Answer
Gradual size decrease across the lanthanoids.
Question 4.8
State characteristics of transition elements, explain the name, and identify d-block elements not regarded as transition elements.
Steps only
Part-filled d shells give characteristic properties; Zn, Cd and Hg have full d shells in atoms and common ions.
Answer
Zn, Cd and Hg are not transition elements by the strict definition.
Question 4.9
How do transition-element electronic configurations differ from those of non-transition elements?
Steps only
Transition elements fill (n−1)d; main-group elements fill s or p.
Answer
They fill inner d orbitals.
Question 4.10
What oxidation states do lanthanoids show?
Steps only
+3 is usual; +2 and +4 occur for some elements.
Answer
+3, sometimes +2 or +4.
Question 4.11
Give reasons: (i) paramagnetism (ii) high atomisation enthalpy (iii) coloured compounds (iv) catalytic activity.
Steps only
Unpaired d electrons cause magnetism and colour; strong metal bonding raises atomisation energy; changing oxidation states and surfaces aid catalysis.
Answer
These properties arise mainly from partially filled d orbitals.
Question 4.12
What are interstitial compounds, and why are they common for transition metals?
Steps only
Small atoms sit in lattice gaps, e.g. TiC and Fe₃H.
Answer
Interstitial compounds contain atoms in the metal lattice gaps.
Question 4.13
How does oxidation-state variation in transition metals differ from that in non-transition metals? Give examples.
Steps only
Close ns and (n−1)d energies let transition metals use different numbers of electrons.
Answer
Transition metals often show many states one unit apart.
Question 4.14
Describe how K₂Cr₂O₇ is prepared from chromite ore and what raising pH does to a dichromate solution.
Steps only
Ore → chromate → acidified dichromate → K₂Cr₂O₇ crystals; alkali converts dichromate to chromate.
Answer
Higher pH shifts orange dichromate to yellow chromate.
Question 4.15
Explain dichromate's oxidising action and write ionic equations with iodide, Fe²⁺ and H₂S.
Steps only
Use Cr₂O₇²⁻+14H⁺+6e⁻→2Cr³⁺+7H₂O and add the oxidation half-reaction.
Answer
Equations are given for I⁻, Fe²⁺ and H₂S.
Question 4.16
Describe KMnO₄ preparation and its acidified reactions with Fe²⁺, SO₂ and oxalic acid.
Steps only
Make manganate from MnO₂, then oxidise it to permanganate; acidic MnO₄⁻ becomes Mn²⁺.
Answer
The balanced reactions are shown in the answer.
Question 4.17
Using the given potentials, compare (i) Fe³⁺ stability with Cr³⁺/Mn³⁺ and (ii) ease of oxidation of Fe, Cr and Mn metals.
Steps only
Use E° signs: positive M³⁺/M²⁺ favours reduction; more negative M²⁺/M favours metal oxidation.
Answer
Fe³⁺ stability: Cr³⁺ > Fe³⁺ > Mn³⁺; oxidation ease: Mn > Cr > Fe.
Question 4.18
Which aqueous ions among Ti³⁺, V³⁺, Cu⁺, Sc³⁺, Mn²⁺, Fe³⁺ and Co²⁺ are coloured? Explain.
Steps only
Partly filled d shells give colour; d⁰ and d¹⁰ ions are colourless.
Answer
Coloured: Ti³⁺, V³⁺, Mn²⁺, Fe³⁺, Co²⁺. Colourless: Cu⁺, Sc³⁺.
Question 4.19
Compare the stability of the +2 oxidation state across the first transition series.
Steps only
+2 is common; d⁵ Mn²⁺, d¹⁰ Zn²⁺ and strong hydration cause notable stability.
Answer
Stability varies; Mn²⁺ and Zn²⁺ are especially favoured.
Question 4.20
Compare actinoids and lanthanoids in electronic configuration, size, oxidation states and reactivity.
Steps only
4f/+3 is typical for lanthanoids; 5f/multiple states, greater contraction and radioactivity mark actinoids.
Answer
Actinoids have more variable chemistry than lanthanoids.
Question 4.21
Explain (i) Cr²⁺ is reducing but Mn³⁺ oxidising, (ii) Co²⁺ is stable in water but complexing agents help oxidise it, (iii) d¹ ions are unstable.
Steps only
Stable product states explain the redox behaviour; ligands can stabilise Co³⁺.
Answer
Cr²⁺ is a reducing agent; Mn³⁺ is an oxidising agent.
Question 4.22
Define disproportionation and give two aqueous examples.
Steps only
One oxidation state is both oxidised and reduced.
Answer
Examples: Cu⁺ and MnO₄²⁻ disproportionate.
Question 4.23
Which first-row transition metal most often shows +1, and why?
Steps only
Cu loses its 4s electron to form stable 3d¹⁰ Cu⁺.
Answer
Copper.
Question 4.24
Count unpaired electrons in gaseous Mn³⁺, Cr³⁺, V³⁺ and Ti³⁺. Which is most stable in water?
Steps only
d⁴, d³, d², d¹ give 4, 3, 2, 1 unpaired electrons.
Answer
Cr³⁺ is especially stable in water.
Question 4.25
Explain with examples: (i) lowest oxides are basic and highest amphoteric/acidic (ii) highest oxidation states occur in oxides/fluorides (iii) high states occur in oxoanions.
Steps only
Higher oxidation states increase oxide acidity; O/F and oxoanion bonds stabilise high states.
Answer
Examples: V₂O₃/V₂O₅, CrO₄²⁻, MnO₄⁻.
Question 4.26
Outline preparation of (i) K₂Cr₂O₇ from chromite and (ii) KMnO₄ from pyrolusite.
Steps only
Chromite: chromate → dichromate → potassium dichromate. Pyrolusite: manganate → permanganate.
Answer
These are the preparation sequences.
Question 4.27
What is an alloy? Name a lanthanoid-containing alloy and state its uses.
Steps only
Mischmetall contains mostly lanthanoids and is used in lighter flints.
Answer
Mischmetall.
Question 4.28
What are inner transition elements? Which of atomic numbers 29, 59, 74, 95, 102 and 104 are inner transition elements?
Steps only
59, 95 and 102 lie in the f-block.
Answer
59, 95, 102.
Question 4.29
Why is actinoid chemistry less regular than lanthanoid chemistry? Give oxidation-state examples.
Steps only
Close 5f, 6d and 7s energies allow varied oxidation states.
Answer
Actinoid chemistry is more variable and complex.
Question 4.30
Name the last actinoid, give its configuration, and state its likely oxidation state.
Steps only
Lr is the last actinoid and commonly forms Lr³⁺.
Answer
Lawrencium; +3.
Question 4.31
Use Hund's rule to find the configuration and spin-only magnetic moment of Ce³⁺.
Steps only
n=1; μ=√(1×3)=1.73 BM.
Answer
[Xe]4f¹; 1.73 BM.
Question 4.32
Name lanthanoids that show +4 and +2 states and link these states to configurations.
Steps only
Ce⁴⁺ is f⁰, Eu²⁺ f⁷ and Yb²⁺ f¹⁴; related states occur for Pr, Tb, Dy, Sm and Tm.
Answer
+4: Ce, Pr, Tb, Dy; +2: Sm, Eu, Tm, Yb.
Question 4.33
Compare actinoids and lanthanoids in configuration, oxidation states and reactivity.
Steps only
4f/+3 is typical of lanthanoids; 5f/multiple states/radioactivity mark actinoids.
Answer
Actinoids are more variable and radioactive.
Question 4.34
Write configurations for atomic numbers 61, 91, 101 and 109.
Steps only
Use [Xe] for Pm and [Rn] for the actinoids/heavier element.
Answer
Pm [Xe]4f⁵6s²; Pa [Rn]5f²6d¹7s²; Md [Rn]5f¹³7s²; Mt [Rn]5f¹⁴6d⁷7s².
Question 4.35
Compare first-row transition metals with their second- and third-row partners by configurations, oxidation states, ionisation enthalpies and size.
Steps only
3d/4d/5d filling distinguishes the rows; 4d and 5d sizes are similar due to lanthanoid contraction.
Answer
The three rows share trends but differ in oxidation states and size.
Question 4.36
Give 3d counts for Ti²⁺, V²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺ and Cu²⁺, and describe their high-spin octahedral filling in water.
Steps only
Counts: d², d³, d³, d⁵, d⁶, d⁵, d⁷, d⁸, d⁹; weak-field water gives high spin.
Answer
The electron counts and unpaired counts are listed in the answer.
Question 4.37
Comment on how the first transition series differs from heavier transition series.
Steps only
Heavier transition elements have more extended orbitals and often show higher coordination and oxidation states.
Answer
The first row often differs in bonding and oxidation-state behaviour.
Question 4.38
What can be inferred from magnetic moments: K₄[Mn(CN)₆] 2.2 BM; [Fe(H₂O)₆]²⁺ 5.3 BM; K₂[MnCl₄] 5.9 BM?
Steps only
The moments correspond approximately to 1, 4 and 5 unpaired electrons.
Answer
Low-spin Mn complex; high-spin Fe²⁺ and Mn²⁺ complexes.