JEE Chemistry The D and F Block Elements MCQs Set 11

Answer: (c) 5

Explanation:
1. Cr is [Ar] 3d⁵ 4s¹; removing the 4s electron gives \( \ce{Cr^+} \) = [Ar] 3d⁵.
2. Five d electrons occupy five orbitals singly, so there are 5 unpaired electrons.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (d) +6

Explanation:
1. Cr has six valence electrons (3d⁵ 4s¹).
2. All six can be used, so the maximum oxidation state is +6, as in chromates and dichromates.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (b) They show variable oxidation states

Explanation:
1. Transition elements use both (n-1)d and ns electrons in bonding, which gives several oxidation states.
2. They are fairly unreactive, have high melting points and are only moderately electropositive.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) Cr

Explanation:
1. \( \ce{Cr^{3+}} \) salts are green or violet, while chromate (yellow) and dichromate (orange) contain Cr(VI).
2. Hence the metal is Cr.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (d) Mn

Explanation:
1. Mn has the configuration 3d⁵ 4s² with seven valence electrons.
2. It reaches +7 in \( \ce{MnO4^-} \); Co, Cr and V cannot exceed +3, +6 and +5 respectively.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) the atomic weight

Explanation:
1. \( \ce{Fe^{2+} -> Fe^{3+} + e^-} \) involves one electron.
2. Equivalent weight = atomic weight / 1 = the atomic weight.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) Os

Explanation:
1. Osmium has the highest known density, about 22.6 g/cm³.
2. Au is about 19.3, Hg about 13.6 and Pb about 11.3 g/cm³.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) (n-1)d and ns orbitals

Explanation:
1. The (n-1)d and ns energy levels are very close.
2. Electrons from both sets can take part in bonding, giving several oxidation states.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (d) transition elements

Explanation:
1. Partially filled d orbitals allow d-d transitions that absorb visible light.
2. So transition-metal ions generally give coloured salts.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) Cu

Explanation:
1. Na and Ca are s-block elements and Ar is p-block.
2. Cu (3d¹⁰ 4s¹) is a d-block element.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) iron

Explanation:
1. Z = 26 corresponds to [Ar] 3d⁶ 4s², which is iron.
2. Mn is 25 and Kr is 36.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (b) Nickel

Explanation:
1. Nickel reacts with CO at about 330 K to give volatile \( \ce{Ni(CO)4} \).
2. The carbonyl decomposes on heating at about 450 K to give pure nickel (Mond process).

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) Copper, silver and gold

Explanation:
1. Coins have traditionally been made of the group 11 metals.
2. These are Cu, Ag and Au.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (b) 2, 8, 18, 1

Explanation:
1. Copper has 29 electrons: 2, 8, 18, 1.
2. 2, 8, 1 is sodium.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (a) 24

Explanation:
1. The neutral atom has three more electrons than the ion, so 18 + 3 + 3 = 24 electrons.
2. Z = 24 is chromium, and \( \ce{Cr^{3+}} \) is 3d³.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (d) ability to adopt multiple oxidation states and to form complexes

Explanation:
1. Variable oxidation states let them form unstable intermediates, and complex formation lets them bind reactants on the surface.
2. Both features lower the activation energy of reactions.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) \( \ce{Fe^{3+}} \)

Explanation:
1. Unpaired electrons: \( \ce{V^{3+}} \) (3d²) = 2, \( \ce{Mn^{3+}} \) (3d⁴) = 4, \( \ce{Fe^{3+}} \) (3d⁵) = 5, \( \ce{Cu^{2+}} \) (3d⁹) = 1.
2. Magnetic moment grows with unpaired electrons, so \( \ce{Fe^{3+}} \) is highest (about 5.92 BM).

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) unpaired d electrons

Explanation:
1. Colour arises from d-d transitions, which need unpaired or partly filled d orbitals.
2. Ions with d⁰ or d¹⁰ configurations are colourless.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (b) \( \ce{Fe^{2+}} \)

Explanation:
1. Zn (3d¹⁰) has 0, \( \ce{Fe^{2+}} \) (3d⁶) has 4, \( \ce{Ni^{3+}} \) (3d⁷) has 3 and \( \ce{Cu^+} \) (3d¹⁰) has 0.
2. So \( \ce{Fe^{2+}} \) has the most.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (c) \( \ce{Fe^{3+}} \)

Explanation:
1. \( \ce{Al(OH)3} \), \( \ce{Cr(OH)3} \) and \( \ce{Zn(OH)2} \) dissolve in both acids and strong alkalis.
2. \( \ce{Fe(OH)3} \) dissolves only in acids, so it is basic.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (a) \( \ce{Fe} \)

Explanation:
1. Mercury amalgamates with most metals, e.g. Ag, Zn, Cu, Au.
2. Iron (and Co, Ni, Pt in practice) is not wetted by mercury, so iron flasks are used to store it.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (a) \( \ce{Mn^{2+}} \)

Explanation:
1. \( \ce{Mn^{2+}} \) is 3d⁵ (5 unpaired), \( \ce{Fe^{2+}} \) 3d⁶ (4), \( \ce{Co^{2+}} \) 3d⁷ (3) and \( \ce{Ni^{2+}} \) 3d⁸ (2).
2. So \( \ce{Mn^{2+}} \) has the most.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (b) its d orbital is complete

Explanation:
1. Zn is 3d¹⁰ 4s² and the stable d¹⁰ set does not take part in bonding.
2. So Zn shows only the +2 state.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (d) They do not form coordination compounds

Explanation:
1. Transition metals form a very large number of complexes because of small, highly charged ions and vacant d orbitals.
2. So statement (d) is false.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.

Answer: (d) \( \ce{Cu^+} \)

Explanation:
1. \( \ce{Cu^+} \) is 3d¹⁰ with no d-d transitions, so it is colourless.
2. The other three have partly filled d subshells and are coloured.

Teacher's Note:
1. Write the electronic configuration of the species first; most d-block questions follow from it.
2. Compare options using trends (oxidation states, size, magnetism) rather than memorising isolated facts.