Assertion A: Aqueous Cu²⁺ salts are coloured. Reason R: A neutral copper atom has the configuration [Ar] 3d¹⁰ 4s¹. Choose the correct answer.

Both A and R are correct but R is not the correct explanation of A

A is correct but R is not correct

Both A and R are correct and R is the correct explanation of A

A is not correct but R is correct

Lanthanoid contraction is caused by

imperfect shielding of one 4f electron by another

the strong shielding by the 5d electrons

the rise in the number of 6s electrons along the series

the decrease in nuclear charge along the series

d- and f-Block Elements

39 NEET-UG practice questions on d- and f-Block Elements, part of Chemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
Pyrolusite is fused with KOH in air to give a green compound X. On acidification, X gives a purple compound Y along with MnO₂. Identify X and Y.
1. AX = K₂MnO₄; Y = Mn₂O₇
2. BX = K₂MnO₄; Y = KMnO₄
3. CX = KMnO₄; Y = K₂MnO₄
4. DX = Mn₂O₇; Y = KMnO₄
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Answer: B · X = K₂MnO₄; Y = KMnO₄
2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O gives green manganate, with Mn at +6. In acid it disproportionates: 3MnO₄²⁻ + 4H⁺ → 2MnO₄⁻ + MnO₂ + 2H₂O, giving purple permanganate at +7 and MnO₂ at +4.
- A: Mn₂O₇ is an oily covalent oxide, not the purple salt formed here.
- C: Swaps the colours; permanganate is purple and manganate is green.
- D: Mn₂O₇ is not formed by fusing with KOH.
Remember this
Manganate is green and stable in alkali; in neutral or acidic solution it disproportionates to permanganate and MnO₂.
Question 2 · Medium
In neutral or faintly alkaline solution, potassium permanganate oxidises iodide. The manganese and iodine products of this reaction are
1. AMnO₄²⁻ and I₂
2. BMnO₂ and I₂
3. CMn²⁺ and I₂
4. DMnO₂ and IO₃⁻
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Answer: D · MnO₂ and IO₃⁻
2MnO₄⁻ + H₂O + I⁻ → 2MnO₂ + 2OH⁻ + IO₃⁻; the charge is −3 on each side. Mn goes from +7 to +4 and I from −1 to +5.
- A: Manganate needs strongly alkaline medium, and it does not give I₂ here.
- B: Right manganese product, but iodide is oxidised further, to iodate.
- C: These are the products in acidic solution.
Remember this
Permanganate gives Mn²⁺ in acid and MnO₂ in neutral or faintly alkaline medium; here iodide becomes iodate.
Question 3 · Medium
Arrange these lanthanoid ions in increasing order of ionic radius. A. Nd³⁺ B. Lu³⁺ C. La³⁺ D. Gd³⁺
1. AD, B, A, C
2. BB, D, A, C
3. CB, A, D, C
4. DC, A, D, B
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Answer: B · B, D, A, C
The atomic numbers rise from La (57) through Nd (60) and Gd (64) to Lu (71). Lanthanoid contraction makes the M³⁺ radius fall steadily along this sequence.
- A: Places Gd³⁺ below Lu³⁺, ignoring where each lies in the series.
- C: Places Nd³⁺ below Gd³⁺, though it comes earlier in the series.
- D: Gives the decreasing order, the reverse of what is asked.
Remember this
M³⁺ radius falls smoothly across the lanthanoids, so La³⁺ is the largest and Lu³⁺ the smallest.
Question 4 · Medium
Assertion A: Aqueous Cu²⁺ salts are coloured. Reason R: A neutral copper atom has the configuration [Ar] 3d¹⁰ 4s¹. Choose the correct answer.
1. AA is correct but R is not correct
2. BBoth A and R are correct and R is the correct explanation of A
3. CA is not correct but R is correct
4. DBoth A and R are correct but R is not the correct explanation of A
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Answer: D · Both A and R are correct but R is not the correct explanation of A
Both are true, but R describes the neutral atom with a full 3d subshell. The colour comes from Cu²⁺, which is d⁹ and has an unpaired electron available for d-d transitions.
- A: R is true; it is the standard configuration of copper.
- B: R describes the neutral atom; the colour comes from the d⁹ ion.
- C: A is true; Cu²⁺ salts are blue in solution.
Remember this
Colour depends on the d count of the ion, so check the ion and not the neutral atom.
Question 5 · Easy
Lanthanoid contraction is caused by
1. Athe strong shielding by the 5d electrons
2. Bimperfect shielding of one 4f electron by another
3. Cthe rise in the number of 6s electrons along the series
4. Dthe decrease in nuclear charge along the series
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Answer: B · imperfect shielding of one 4f electron by another
Along the series, nuclear charge rises by one with each step while the added 4f electron shields poorly. The effective nuclear charge therefore rises and the size falls.
- A: It is the poor shielding by 4f electrons that matters, not strong 5d shielding.
- C: The 6s electrons remain two throughout the series.
- D: Nuclear charge rises, not falls, along the series.
Remember this
The poor shielding of 4f electrons also makes radii of the 4d and 5d series nearly equal.
Question 6 · Medium
Match List-I with List-II. List-I (ion; Z of Ti = 22, V = 23, Cr = 24, Fe = 26) A. Ti³⁺ B. V³⁺ C. Cr³⁺ D. Fe²⁺ List-II (spin-only moment in BM) I. 3.87 II. 4.90 III. 1.73 IV. 2.83
1. AA-III, B-IV, C-II, D-I
2. BA-III, B-I, C-IV, D-II
3. CA-III, B-IV, C-I, D-II
4. DA-IV, B-III, C-I, D-II
Answer and explanation in LearnFree account
Question 7 · Hard
In acid solution, 30 mL of 0.02 M KMnO₄ just oxidises the Fe²⁺ in a sample. What volume of 0.01 M K₂Cr₂O₇ would be needed for an identical sample in acid solution?
1. A100 mL
2. B60 mL
3. C30 mL
4. D50 mL
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Question 8 · Hard
Given below are two statements: Statement I: Because of lanthanoid contraction, the atomic radii of Zr and Hf differ widely. Statement II: Eu²⁺ acts as a strong oxidising agent because it changes readily to the common +3 state. Choose the correct answer.
1. ABoth Statement I and Statement II are incorrect
2. BStatement I is incorrect but Statement II is correct
3. CBoth Statement I and Statement II are correct
4. DStatement I is correct but Statement II is incorrect
Answer and explanation in LearnFree account
Question 9 · Medium
Which ion is a strong oxidising agent in aqueous solution because its reduction gives a stable half-filled d⁵ configuration?
1. ACr³⁺
2. BV²⁺
3. CMn³⁺
4. DFe²⁺
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Question 10 · Medium
Given below are two statements: Statement I: On acidifying a yellow chromate solution, orange dichromate forms with no change in the oxidation state of chromium. Statement II: In the Cr₂O₇²⁻ ion, two tetrahedra share one corner through a Cr–O–Cr link. Choose the correct answer.
1. ABoth Statement I and Statement II are incorrect
2. BStatement I is correct but Statement II is incorrect
3. CBoth Statement I and Statement II are correct
4. DStatement I is incorrect but Statement II is correct
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Question 11 · Easy
Calculate the spin-only magnetic moment of Fe³⁺. (Z of Fe = 26.)
1. A4.90 BM
2. B3.87 BM
3. C1.73 BM
4. D5.92 BM
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Question 12 · Easy
Atoms of two 3d-series elements hold only one 4s electron in the ground state, unlike the usual 4s² pattern. These two elements are
1. ASc and Zn
2. BMn and Fe
3. CV and Ni
4. DCr and Cu
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Question 13 · Medium
Compared with lanthanoids, actinoids show a wider range of oxidation states mainly because
1. Aactinoids have much smaller atomic radii than lanthanoids
2. Bthe 5f, 6d and 7s levels have comparable energies
3. Cactinoids have no electrons in their 5f subshell
4. Dthe 4f electrons are lost more easily than the 6s electrons
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Question 14 · Hard
In acidic solution, potassium permanganate oxidises both the iron(II) and the oxalate in iron(II) oxalate, FeC₂O₄, to Fe³⁺ and CO₂, being itself reduced to Mn²⁺. How many moles of KMnO₄ are needed to oxidise 1 mol of FeC₂O₄ completely?
1. A1.67
2. B0.4
3. C0.6
4. D0.2
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Question 15 · Medium
Among the aqueous ions below, the one whose spin-only magnetic moment equals 4.90 BM is (atomic numbers: Cr = 24, Mn = 25, Fe = 26, Cu = 29)
1. AFe²⁺
2. BCu²⁺
3. CCr³⁺
4. DMn²⁺
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Question 16 · Medium
Arrange the compounds in increasing order of the oxidation state of manganese. A. KMnO₄ B. MnO₂ C. K₂MnO₄ D. Mn₂O₃
1. AB, D, C, A
2. BB, C, D, A
3. CD, B, A, C
4. DD, B, C, A
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Question 17 · Easy
Which lanthanoid shows a +4 oxidation state in which it is a strong oxidising agent, readily returning to the +3 state?
1. ACerium
2. BGadolinium
3. CYtterbium
4. DEuropium
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Question 18 · Medium
Given below are two statements: Statement I: Zinc, cadmium and mercury are not regarded as transition elements in the strict sense, as they have completely filled d orbitals in the ground state and in their common oxidation states. Statement II: Among the 3d series, zinc has the highest enthalpy of atomisation. Choose the correct answer.
1. AStatement I is incorrect but Statement II is correct
2. BBoth Statement I and Statement II are incorrect
3. CBoth Statement I and Statement II are correct
4. DStatement I is correct but Statement II is incorrect
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Question 19 · Easy
Which of these ions is colourless in aqueous solution?
1. ACu²⁺
2. BTi³⁺
3. CSc³⁺
4. DV³⁺
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Question 20 · Medium
Chromite ore, FeCr₂O₄, is fused with sodium carbonate in free access of air. Which chromium compound is formed in this first step of making potassium dichromate?
1. ANa₂CrO₄
2. BNa₂Cr₂O₇
3. CCr₂O₃
4. DK₂CrO₄
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Question 21 · Easy
Zinc, cadmium and mercury are not regarded as transition elements because
1. Athey have completely filled d orbitals in the atom and in their common ions
2. Bthey have partly filled d orbitals in the atom but not in their ions
3. Cthey always lose d electrons before s electrons
4. Dthey have no electrons at all in their d orbitals
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Question 22 · Hard
Acidified potassium dichromate oxidises Fe²⁺ to Fe³⁺ and Sn²⁺ to Sn⁴⁺. One mole of K₂Cr₂O₇ exactly oxidises a solution containing equal numbers of moles of FeSO₄ and SnCl₂. Assuming chloride is not oxidised, how many moles of SnCl₂ does the solution contain?
1. A2
2. B1.5
3. C3
4. D6
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Question 23 · Easy
Which element of the first transition series shows the largest number of oxidation states?
1. AScandium
2. BManganese
3. CChromium
4. DIron
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Question 24 · Medium
What happens when sodium hydroxide solution is added to an aqueous solution of potassium dichromate?
1. AThe solution turns yellow as CrO₄²⁻ forms, and chromium stays in the +6 state
2. BThe solution stays orange, since dichromate is stable in alkali
3. CThe solution turns green as Cr³⁺ forms, and chromium is reduced
4. DThe solution turns yellow as CrO₄²⁻ forms, and chromium is oxidised to +7
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Question 25 · Medium
Assertion A: The Cu⁺ ion is unstable in aqueous solution and disproportionates into Cu²⁺ and Cu. Reason R: The hydration enthalpy of Cu²⁺ is much more negative than that of Cu⁺, which more than compensates for the second ionisation enthalpy of copper. Choose the correct answer.
1. AA is correct but R is not correct
2. BBoth A and R are correct but R is not the correct explanation of A
3. CBoth A and R are correct and R is the correct explanation of A
4. DA is not correct but R is correct
Answer and explanation in LearnFree account

14 more d- and f-Block Elements questions

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Study Chemistry

d- and f-Block Elements

Pyrolusite is fused with KOH in air to give a green compound X. On acidification, X gives a purple compound Y along with MnO₂. Identify X and Y.

In neutral or faintly alkaline solution, potassium permanganate oxidises iodide. The manganese and iodine products of this reaction are

Arrange these lanthanoid ions in increasing order of ionic radius. A. Nd³⁺ B. Lu³⁺ C. La³⁺ D. Gd³⁺

Assertion A: Aqueous Cu²⁺ salts are coloured. Reason R: A neutral copper atom has the configuration [Ar] 3d¹⁰ 4s¹. Choose the correct answer.

Lanthanoid contraction is caused by

Match List-I with List-II. List-I (ion; Z of Ti = 22, V = 23, Cr = 24, Fe = 26) A. Ti³⁺ B. V³⁺ C. Cr³⁺ D. Fe²⁺ List-II (spin-only moment in BM) I. 3.87 II. 4.90 III. 1.73 IV. 2.83

In acid solution, 30 mL of 0.02 M KMnO₄ just oxidises the Fe²⁺ in a sample. What volume of 0.01 M K₂Cr₂O₇ would be needed for an identical sample in acid solution?

Given below are two statements: Statement I: Because of lanthanoid contraction, the atomic radii of Zr and Hf differ widely. Statement II: Eu²⁺ acts as a strong oxidising agent because it changes readily to the common +3 state. Choose the correct answer.

Which ion is a strong oxidising agent in aqueous solution because its reduction gives a stable half-filled d⁵ configuration?

Given below are two statements: Statement I: On acidifying a yellow chromate solution, orange dichromate forms with no change in the oxidation state of chromium. Statement II: In the Cr₂O₇²⁻ ion, two tetrahedra share one corner through a Cr–O–Cr link. Choose the correct answer.

Calculate the spin-only magnetic moment of Fe³⁺. (Z of Fe = 26.)

Atoms of two 3d-series elements hold only one 4s electron in the ground state, unlike the usual 4s² pattern. These two elements are

Compared with lanthanoids, actinoids show a wider range of oxidation states mainly because

In acidic solution, potassium permanganate oxidises both the iron(II) and the oxalate in iron(II) oxalate, FeC₂O₄, to Fe³⁺ and CO₂, being itself reduced to Mn²⁺. How many moles of KMnO₄ are needed to oxidise 1 mol of FeC₂O₄ completely?

Among the aqueous ions below, the one whose spin-only magnetic moment equals 4.90 BM is (atomic numbers: Cr = 24, Mn = 25, Fe = 26, Cu = 29)

Arrange the compounds in increasing order of the oxidation state of manganese. A. KMnO₄ B. MnO₂ C. K₂MnO₄ D. Mn₂O₃

Which lanthanoid shows a +4 oxidation state in which it is a strong oxidising agent, readily returning to the +3 state?

Which of these ions is colourless in aqueous solution?

Chromite ore, FeCr₂O₄, is fused with sodium carbonate in free access of air. Which chromium compound is formed in this first step of making potassium dichromate?

Zinc, cadmium and mercury are not regarded as transition elements because

Acidified potassium dichromate oxidises Fe²⁺ to Fe³⁺ and Sn²⁺ to Sn⁴⁺. One mole of K₂Cr₂O₇ exactly oxidises a solution containing equal numbers of moles of FeSO₄ and SnCl₂. Assuming chloride is not oxidised, how many moles of SnCl₂ does the solution contain?

Which element of the first transition series shows the largest number of oxidation states?

What happens when sodium hydroxide solution is added to an aqueous solution of potassium dichromate?

Assertion A: The Cu⁺ ion is unstable in aqueous solution and disproportionates into Cu²⁺ and Cu. Reason R: The hydration enthalpy of Cu²⁺ is much more negative than that of Cu⁺, which more than compensates for the second ionisation enthalpy of copper. Choose the correct answer.