JEE Chemistry The D and F Block Elements MCQs Set 06

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Chapter-wise Objective Questions: The D and F Block Elements

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Multiple Choice Questions

Question 1: For a catalyst, which condition is not essential?
(a) Variable valency
(b) High ionisation energy
(c) Empty orbitals
(d) Free valency on the surface
Show Answer & Explanation

Answer: (b) High ionisation energy

Explanation:
1. Transition metals are good catalysts because of variable valency, vacant d orbitals and free valencies on the surface.
2. They do not need a high ionisation energy.

Teacher's Note:
1. Catalytic action needs adsorption and variable oxidation states.

Question 2: To which series does the transition element from Z = 39 to Z = 48 belong?
(a) 3d series
(b) 4d series
(c) 5d series
(d) 6d series
Show Answer & Explanation

Answer: (b) 4d series

Explanation:
1. These are yttrium to cadmium, in which the 4d orbitals are filled.

Teacher's Note:
1. Z = 21-30 is 3d, 39-48 is 4d, 57 and 72-80 is 5d.

Question 3: KMnO4 with conc. H2SO4 forms a compound (X) which decomposes explosively on heating to give (Y). X and Y are respectively
(a) Mn2O7, MnO2
(b) Mn2O, Mn2O3
(c) MnSO4, Mn2O3
(d) Mn2O3, MnO2
Show Answer & Explanation

Answer: (a) Mn2O7, MnO2

Explanation:
1. KMnO4 and cold conc. H2SO4 give the green oily Mn2O7.
2. It explodes on heating to MnO2, O2 (and ozone).

Teacher's Note:
1. Recall the electronic configuration of the ion.
2. Count unpaired electrons for magnetic questions.

Question 4: Which pair of ions is colourless?
(a) Mn3+, Co3+
(b) Fe3+, Cr3+
(c) Zn2+, Sc3+
(d) Ti2+, Cu2+
Show Answer & Explanation

Answer: (c) Zn2+, Sc3+

Explanation:
1. Zn2+ (3d10) and Sc3+ (3d0) have no unpaired d electrons, so there is no d-d transition.

Teacher's Note:
1. Colour needs a partly filled d subshell.

Question 5: The green coloured powder blown in air in fireworks (from ammonium dichromate) is
(a) Cr2O3
(b) CrO2
(c) Cr2O4
(d) CrO3
Show Answer & Explanation

Answer: (a) Cr2O3

Explanation:
1. (NH4)2Cr2O7 decomposes to N2, water and green Cr2O3.

Teacher's Note:
1. This is the volcano reaction.

Question 6: In Cr2O7 2- <-> 2CrO4 2-, the reagents X and Y are respectively
(a) X = OH-, Y = H+
(b) X = H+, Y = OH-
(c) X = OH-, Y = H2O2
(d) X = H2O2, Y = OH-
Show Answer & Explanation

Answer: (a) X = OH-, Y = H+

Explanation:
1. Alkali converts dichromate (orange) to chromate (yellow); acid reverses it.

Teacher's Note:
1. Orange in acid, yellow in base.

Question 7: In the estimation of oxalic acid versus KMnO4, the self indicator is
(a) KMnO4
(b) Oxalic acid
(c) K2SO4
(d) MnSO4
Show Answer & Explanation

Answer: (a) KMnO4

Explanation:
1. The permanganate colour persists after the end point, so it acts as its own indicator.

Teacher's Note:
1. No external indicator is needed.

Question 8: The higher oxidation states of transition elements are found in combination with A and B, which are
(a) F, O
(b) O, N
(c) O, Cl
(d) F, Cl
Show Answer & Explanation

Answer: (a) F, O

Explanation:
1. Only the most electronegative elements, fluorine and oxygen, can stabilise the highest oxidation states.

Teacher's Note:
1. Examples: MnO4-, OsF6.

Question 9: The magnetic moment of Xn+ is sqrt(24) B.M. The number of unpaired electrons and n respectively are (Atomic number = 26)
(a) 4, 3
(b) 3, 5
(c) 4, 2
(d) 4, 1
Show Answer & Explanation

Answer: (c) 4, 2

Explanation:
1. \( \sqrt{n(n+2)}=\sqrt{24} \) gives 4 unpaired electrons.
2. Fe2+ (3d6) has 4 unpaired electrons, so n = 2.

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

Question 10: The product of oxidation of I- with MnO4- in alkaline medium is
(a) IO3-
(b) I2
(c) IO-
(d) IO4-
Show Answer & Explanation

Answer: (a) IO3-

Explanation:
1. In alkaline medium permanganate oxidises iodide to iodate (and is reduced to MnO2).

Teacher's Note:
1. Neutral or alkaline: MnO2 and IO3-.

Question 11: Copper becomes green when exposed to moist air for a long period because of
(a) A layer of cupric oxide
(b) A layer of basic carbonate of copper
(c) A layer of cupric hydroxide
(d) (1) and (3) both
Show Answer & Explanation

Answer: (b) A layer of basic carbonate of copper

Explanation:
1. Copper reacts with CO2 and moisture to form green basic copper carbonate.

Teacher's Note:
1. Verdigris.

Question 12: Which oxide of chromium is amphoteric?
(a) CrO
(b) Cr2O3
(c) CrO3
(d) CrO5
Show Answer & Explanation

Answer: (b) Cr2O3

Explanation:
1. CrO is basic, CrO3 is acidic and Cr2O3 is amphoteric.

Teacher's Note:
1. Acidity rises with oxidation state.

Question 13: Compared to Cu2+ having 3d9 configuration, Cu+ having 3d10 configuration in aqueous solution is
(a) More stable
(b) Equally stable
(c) Less stable
(d) Stability depends on the copper salt
Show Answer & Explanation

Answer: (c) Less stable

Explanation:
1. The higher hydration enthalpy of Cu2+ outweighs the second ionisation energy, so Cu+ disproportionates in water.

Teacher's Note:
1. 2Cu+ gives Cu2+ and Cu.

Question 14: Pick out the wrong statement.
(a) K2Cr2O7 reduces ferric sulphate to ferrous sulphate
(b) Iron does not form amalgam
(c) A permanent magnet is made of an alloy called Alnico
(d) In the lanthanides the ionic radius decreases from La3+ to Lu3+
Show Answer & Explanation

Answer: (a) K2Cr2O7 reduces ferric sulphate to ferrous sulphate

Explanation:
1. Dichromate is an oxidising agent: it oxidises ferrous to ferric, not the reverse.

Teacher's Note:
1. Cr(VI) is reduced to Cr(III).

Question 15: CrO3 is red or orange in colour. The nature of the oxide is
(a) Acidic
(b) Basic
(c) Amphoteric
(d) Neutral
Show Answer & Explanation

Answer: (a) Acidic

Explanation:
1. Chromium in its highest oxidation state, +6, gives an acidic oxide.

Teacher's Note:
1. It forms chromic acid with water.

Question 16: Cl2 gas is obtained by the various reactions below, but not by
(a) KMnO4 + conc. HCl
(b) KCl + K2Cr2O7 + conc. H2SO4
(c) MnO2 + conc. HCl
(d) KCl + F2
Show Answer & Explanation

Answer: (b) KCl + K2Cr2O7 + conc. H2SO4

Explanation:
1. KCl, K2Cr2O7 and conc. H2SO4 give red chromyl chloride vapours.
2. The others liberate chlorine.

Teacher's Note:
1. Chromyl chloride test.

Question 17: The maximum magnetic moment is shown by
(a) d5
(b) d6
(c) d3
(d) d8
Show Answer & Explanation

Answer: (a) d5

Explanation:
1. d5 has five unpaired electrons.

Teacher's Note:
1. n(n+2) is largest for five unpaired electrons.

Question 18: Disproportionation can be shown by
(a) MnO4 2- in acidic medium
(b) Cu+ in aqueous medium
(c) Cl2 in alkaline medium
(d) All of these
Show Answer & Explanation

Answer: (d) All of these

Explanation:
1. Manganate, Cu+ and Cl2 each undergo self oxidation and reduction in the stated media.

Teacher's Note:
1. Intermediate oxidation states disproportionate.

Question 19: The basic character of the transition metal monoxides follows the order (Ti 22, V 23, Cr 24, Fe 26)
(a) TiO > FeO > VO > CrO
(b) TiO > VO > CrO > FeO
(c) VO > CrO > TiO > FeO
(d) CrO > VO > FeO > TiO
Show Answer & Explanation

Answer: (b) TiO > VO > CrO > FeO

Explanation:
1. Basic strength decreases as the metal-oxygen bond becomes more covalent, with the ionic radius decreasing from Ti to Fe.

Teacher's Note:
1. Radius falls across the series.

Question 20: Which reaction is used to estimate copper volumetrically?
(a) 2Cu2+ + 4F- gives Cu2F2 + F2
(b) Cu2+ + 4NH3 gives [Cu(NH3)4]2+
(c) 2Cu2+ + 2CNS- + SO2 + 2H2O gives Cu2(CNS)2 + H2SO4 + 2H+
(d) 2Cu2+ + 4I- gives Cu2I2 + I2
Show Answer & Explanation

Answer: (d) 2Cu2+ + 4I- gives Cu2I2 + I2

Explanation:
1. The liberated iodine is titrated with hypo (thiosulphate).

Teacher's Note:
1. Iodometric estimation.

Question 21: The atomic size of gold is almost the same as that of silver. It is due to
(a) The same crystal structure
(b) Almost the same electropositive character
(c) Transition metals contraction in a series
(d) The effect of lanthanide contraction
Show Answer & Explanation

Answer: (d) The effect of lanthanide contraction

Explanation:
1. The poor shielding by 4f electrons compensates the extra shell of gold.

Teacher's Note:
1. Lanthanide contraction.

Question 22: Which statement is incorrect?
(a) In d-block elements oxidation states differ by unity
(b) In p-block metals oxidation states differ by two units
(c) In a group of p-block lower oxidation states are favoured by the heavier members
(d) In a group of d-block higher oxidation states are favoured by the lighter members
Show Answer & Explanation

Answer: (d) In a group of d-block higher oxidation states are favoured by the lighter members

Explanation:
1. In the d-block, higher oxidation states are favoured by the heavier members.

Teacher's Note:
1. Opposite to the p-block trend.

Question 23: Which is the correct order of oxidising character?
(a) CrO3 > MoO3
(b) K2Cr2O7 > KMnO4
(c) Fe(CO)5 > Mn(CO)5
(d) V2O3 > V2O5
Show Answer & Explanation

Answer: (a) CrO3 > MoO3

Explanation:
1. Stability of the highest oxidation state increases down the group, so Cr(VI) is more oxidising than Mo(VI).

Teacher's Note:
1. Higher oxidation state: stronger oxidant for the lighter member.

Question 24: Which of the following 3d configurations exhibits the largest number of oxidation states?
(a) [Ar] 3d8 4s2
(b) [Ar] 3d10 4s1
(c) [Ar] 3d5 4s2
(d) [Ar] 3d7 4s2
Show Answer & Explanation

Answer: (c) [Ar] 3d5 4s2

Explanation:
1. Manganese (3d5 4s2) shows oxidation states +2 to +7.

Teacher's Note:
1. The middle of the series shows the most states.

Question 25: Which of the following statements about interstitial compounds is incorrect?
(a) They are chemically inert
(b) They are soft and nonconductive
(c) They retain metallic conductivity
(d) They have high melting points
Show Answer & Explanation

Answer: (b) They are soft and nonconductive

Explanation:
1. Interstitial compounds are hard and conduct like metals.

Teacher's Note:
1. Carbides and nitrides of transition metals.

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

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