JEE Chemistry The D and F Block Elements MCQs Set 07

Chemistry Objective Questions and Answers: The D and F Block Elements

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Multiple Choice Questions

Question 1: Which pair has the same value of spin-only magnetic moment?
(a) Cu+, Cu2+
(b) Co3+, Fe2+
(c) Ti3+, V2+
(d) Sc2+, Zn2+
Show Answer & Explanation

Answer: (b) Co3+, Fe2+

Explanation:
1. Co3+ and Fe2+ are both d6 with 4 unpaired electrons.

Teacher's Note:
1. Count unpaired electrons.

Question 2: The elements from thorium (90) to lawrencium (103), in which 5f energy levels are filled up, are called
(a) Lanthanides
(b) Rare earths
(c) Actinides
(d) Transuranics
Show Answer & Explanation

Answer: (c) Actinides

Explanation:
1. They are the actinides, the second inner transition series.

Teacher's Note:
1. 5f series.

Question 3: Which element does not show a +4 oxidation state?
(a) Ti
(b) Zr
(c) La
(d) Pt
Show Answer & Explanation

Answer: (c) La

Explanation:
1. Lanthanum shows only +3.

Teacher's Note:
1. Group 3 does not go beyond +3.

Question 4: With an increase in atomic number the ionic radii of actinides
(a) Contract slightly
(b) Increase gradually
(c) Show no change
(d) Change irregularly
Show Answer & Explanation

Answer: (a) Contract slightly

Explanation:
1. Actinoid contraction results from the poor shielding of 5f electrons.

Teacher's Note:
1. Similar to lanthanoid contraction.

Question 5: Cerium can show the +4 oxidation state because
(a) It resembles alkali metals
(b) It has a very low value of I.E.
(c) Of its tendency to attain the noble gas configuration of xenon
(d) Of its tendency to attain 4f7 configuration
Show Answer & Explanation

Answer: (c) Of its tendency to attain the noble gas configuration of xenon

Explanation:
1. Ce4+ has the 4f0 xenon core.

Teacher's Note:
1. Ce(IV) is a strong oxidant.

Question 6: In aqueous solution, Eu2+ acts as
(a) An oxidising agent
(b) A reducing agent
(c) Both
(d) None of these
Show Answer & Explanation

Answer: (b) A reducing agent

Explanation:
1. Eu2+ (4f7) readily loses an electron to become the stable Eu3+.

Teacher's Note:
1. Eu2+ is a reducing agent.

Question 7: The maximum oxidation state shown by actinides is
(a) +6
(b) +7
(c) +5
(d) +4
Show Answer & Explanation

Answer: (b) +7

Explanation:
1. Neptunium and plutonium show +7.

Teacher's Note:
1. Actinides reach +7.

Question 8: The outer electronic configuration of gadolinium (Z = 64) is
(a) 4f7 5d1 6s2
(b) 4f8 5d0 6s2
(c) 4f8 5d0 6s1
(d) 4f7 5d0 6s2
Show Answer & Explanation

Answer: (a) 4f7 5d1 6s2

Explanation:
1. The half-filled 4f7 subshell is stable, so the next electron goes to 5d.

Teacher's Note:
1. Gd: 4f7 5d1 6s2.

Question 9: The most characteristic oxidation state of lanthanides is
(a) +2
(b) +3
(c) +4
(d) None of these
Show Answer & Explanation

Answer: (b) +3

Explanation:
1. Lanthanides commonly show +3.

Teacher's Note:
1. Ln3+.

Question 10: The common oxidation state of actinides is
(a) +4
(b) +3
(c) +5
(d) +6
Show Answer & Explanation

Answer: (b) +3

Explanation:
1. +3 is common to all actinides.

Teacher's Note:
1. Like lanthanides.

Question 11: Which pair of elements has almost similar size?
(a) Ti (22) and Zr (40)
(b) Nb (41) and Ta (73)
(c) Y (39) and La (57)
(d) Ca (20) and Ir (31)
Show Answer & Explanation

Answer: (b) Nb (41) and Ta (73)

Explanation:
1. Because of the lanthanide contraction, 4d and 5d elements of the same group have similar radii.

Teacher's Note:
1. Zr-Hf and Nb-Ta.

Question 12: An increase in atomic and ionic radii is expected down a group, but the ionic radius of Hf(IV), 0.75 Å, is almost that of Zr(IV). This is due to
(a) Greater covalency in Hf compounds
(b) Lanthanide contraction
(c) Difference in the co-ordination number
(d) Actinide contraction
Show Answer & Explanation

Answer: (b) Lanthanide contraction

Explanation:
1. The 4f electrons shield poorly, so the 5d series is contracted.

Teacher's Note:
1. Lanthanide contraction.

Question 13: When KMnO4 reacts with Br2 in weak alkaline medium to give bromate, the oxidation state of Mn changes from +7 to
(a) +6
(b) +4
(c) +3
(d) +2
Show Answer & Explanation

Answer: (b) +4

Explanation:
1. In neutral or weakly alkaline medium permanganate is reduced to MnO2.

Teacher's Note:
1. Mn(IV).

Question 14: Which statement is not true?
(a) K2Cr2O7 solution in acidic medium is orange
(b) K2Cr2O7 solution becomes yellow on increasing the pH beyond 7
(c) On passing H2S through acidified K2Cr2O7 solution, a milky colour is observed
(d) Na2Cr2O7 is preferred over K2Cr2O7 in volumetric analysis
Show Answer & Explanation

Answer: (d) Na2Cr2O7 is preferred over K2Cr2O7 in volumetric analysis

Explanation:
1. Potassium dichromate is used as a primary standard because it is not hygroscopic; sodium dichromate is.

Teacher's Note:
1. K salt is preferred.

Question 15: Which does not correctly represent the order of the property indicated?
(a) Ti < V < Cr < Mn : increasing melting points
(b) Ti < V < Mn < Cr : increasing second ionisation enthalpy
(c) Ti < V < Cr < Mn : increasing number of oxidation states
(d) Ti3+ < V3+ < Cr3+ < Mn3+ : increasing magnetic moment
Show Answer & Explanation

Answer: (a) Ti < V < Cr < Mn : increasing melting points

Explanation:
1. The melting points rise to chromium and then fall, so manganese is lower than chromium.

Teacher's Note:
1. Mn has a lower melting point.

Question 16: The catalytic activity of transition metals and their compounds is ascribed mainly to
(a) Their ability to adopt variable oxidation states
(b) Their chemical reactivity
(c) Their magnetic behaviour
(d) Their unfilled d-orbitals
Show Answer & Explanation

Answer: (a) Their ability to adopt variable oxidation states

Explanation:
1. Variable oxidation states allow intermediate compounds to form.

Teacher's Note:
1. Catalysis uses variable valency.

Question 17: The magnetic moment of Cr2+ is nearest to
(a) Fe2+
(b) Mn2+
(c) Co2+
(d) Ni2+
Show Answer & Explanation

Answer: (a) Fe2+

Explanation:
1. Cr2+ (3d4) and Fe2+ (3d6) both have four unpaired electrons.

Teacher's Note:
1. Count unpaired electrons.

Question 18: Which element has the lowest melting point?
(a) Cr
(b) Fe
(c) Ni
(d) Cu
Show Answer & Explanation

Answer: (d) Cu

Explanation:
1. Copper has only one 4s electron to share and its d10 shell does not take part, so its metallic bonding is the weakest of these four.

Teacher's Note:
1. Melting points fall at the end of the series.

Question 19: The maximum number of unpaired electrons is present in
(a) Gd3+
(b) Yb2+
(c) Tb2+
(d) Pm3+
Show Answer & Explanation

Answer: (a) Gd3+

Explanation:
1. Gd3+ is 4f7 with seven unpaired electrons.

Teacher's Note:
1. Half-filled f shell.

Question 20: K2Cr2O7 in acidic medium is converted into
(a) Cr2+
(b) Cr3+
(c) Cr4+
(d) Cr5+
Show Answer & Explanation

Answer: (b) Cr3+

Explanation:
1. Dichromate is reduced to Cr3+.

Teacher's Note:
1. Orange to green.

Question 21: Which metal ion forms an unstable complex with CN-?
(a) Ag(I)
(b) Zn(II)
(c) Cu(II)
(d) Cr(II)
Show Answer & Explanation

Answer: (c) Cu(II)

Explanation:
1. Cu(II) is reduced by cyanide, so the Cu(II) cyanide is unstable.

Teacher's Note:
1. Cu2+ oxidises CN-.

Question 22: Which of the following ions does not exist?
(a) [CuI4]2-
(b) VO4 3-
(c) WO4 2-
(d) CrO4 2-
Show Answer & Explanation

Answer: (a) [CuI4]2-

Explanation:
1. Cu2+ oxidises iodide to iodine, so [CuI4]2- cannot exist.

Teacher's Note:
1. Cu(II) iodide is not stable.

Question 23: A magnetic moment of 2.84 B.M. is given by (Ni 28, Ti 22, Cr 24, Co 27)
(a) Ti3+
(b) Cr2+
(c) Co2+
(d) Ni2+
Show Answer & Explanation

Answer: (d) Ni2+

Explanation:
1. \( \sqrt{n(n+2)}=2.84 \) gives n = 2, and Ni2+ (3d8) has two unpaired electrons.

Teacher's Note:
1. Spin-only formula.

Question 24: Which process does not involve oxidation of iron?
(a) Decolourisation of blue CuSO4 solution by iron
(b) Formation of Fe(CO)5 from Fe
(c) Liberation of H2 from steam by iron at high temperature
(d) Rusting of iron sheets
Show Answer & Explanation

Answer: (b) Formation of Fe(CO)5 from Fe

Explanation:
1. In Fe(CO)5 iron is zero valent.

Teacher's Note:
1. Carbonyls have metal in zero state.

Question 25: Because of the lanthanoid contraction, which pair has nearly the same atomic radii? (atomic numbers in brackets)
(a) Zr (40) and Nb (41)
(b) Zr (40) and Hf (72)
(c) Zr (40) and Ta (73)
(d) Ti (22) and Zr (40)
Show Answer & Explanation

Answer: (b) Zr (40) and Hf (72)

Explanation:
1. Hf follows the lanthanoids, so its radius matches that of Zr.

Teacher's Note:
1. Zr and Hf.

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Multiple Choice Questions (MCQs) for JEE Chemistry The D and F Block Elements

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