JEE Chemistry The D and F Block Elements MCQs Set 05

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

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Multiple Choice Questions

Question 1: Which of the following does NOT reduce \( AgNO_3 \) to metallic silver?
(a) \( H_3PO_4 \)
(b) \( H_3PO_2 \)
(c) \( N_2H_4 \)
(d) \( H_3PO_3 \)
Show Answer & Explanation

Answer: (a) \( H_3PO_4 \)

Explanation:
1. Phosphorus in H3PO4 is already in its highest oxidation state (+5), so it cannot reduce Ag+. H3PO2, H3PO3 and hydrazine are reducing agents.

Teacher's Note:
1. Hypophosphorous acid is the strongest reductant.

Question 2: Iron heated with excess chlorine gives the salt M. M does NOT react with a solution of
(a) \( CH_3COONa \)
(b) \( AgNO_3 \)
(c) \( Na_2S_2O_3 \)
(d) \( SrCl_2 \)
Show Answer & Explanation

Answer: (d) \( SrCl_2 \)

Explanation:
1. M is \( FeCl_3 \). It reacts with acetate (hydrolysis), silver nitrate (AgCl) and thiosulphate (reduction), but not with strontium chloride.

Teacher's Note:
1. No common ion or redox change with SrCl2.

Question 3: The INCORRECT statement about \( K_2MnO_4 \) is
(a) it disproportionates in neutral solution to give \( KMnO_4 \)
(b) it is green
(c) it is stable in acidic medium
(d) it gives brown MnO2 when it disproportionates
Show Answer & Explanation

Answer: (c) it is stable in acidic medium

Explanation:
1. \( 3MnO_4^{2-} + 4H^+ \to 2MnO_4^- + MnO_2 + 2H_2O \): in acid it disproportionates.

Teacher's Note:
1. Manganate is stable only at high pH.

Question 4: The pH values at which \( CrO_4^{2-} \) changes to \( Cr_2O_7^{2-} \) and \( Cr_2O_7^{2-} \) to \( CrO_4^{2-} \) are respectively
(a) 5 and 4
(b) 4 and 8
(c) 4 and 5
(d) 8 and 9
Show Answer & Explanation

Answer: (b) 4 and 8

Explanation:
1. Chromate changes to dichromate in acid (about pH 4) and dichromate changes to chromate in base (about pH 8).

Teacher's Note:
1. Acidic solutions are orange, basic yellow.

Question 5: Which of the following sets shows the correct stability order of the aqueous cations?
(a) \( Mn^{2+}(aq) < Mn^{3+}(aq) \)
(b) \( Co^{2+}(aq) < Co^{3+}(aq) \)
(c) \( Fe^{3+}(aq) < Fe^{2+}(aq) \) in all conditions
(d) \( Cr^{2+}(aq) < Cr^{3+}(aq) \)
Show Answer & Explanation

Answer: (d) \( Cr^{2+}(aq) < Cr^{3+}(aq) \)

Explanation:
1. \( Cr^{3+} \) with \( t_{2g}^3 \) is very stable and \( Cr^{2+} \) is a strong reductant.
2. \( Mn^{3+} \) and \( Co^{3+} \) are strong oxidants, so \( Mn^{2+} \) and \( Co^{2+} \) are more stable in water.

Teacher's Note:
1. Compare the E0 values of the M3+/M2+ couples (Cr: -0.41 V, Mn: +1.57 V, Co: +1.97 V).

Question 6: Which pair of reactions shows that \( Zn(OH)_2 \) is amphoteric?
(a) with NaOH and with water
(b) with water and with \( NH_3 \)
(c) with NaOH and with HCl
(d) with HCl and with \( NH_3 \)
Show Answer & Explanation

Answer: (c) with NaOH and with HCl

Explanation:
1. \( Zn(OH)_2 + 2NaOH \to Na_2[Zn(OH)_4] \) (acidic behaviour).
2. \( Zn(OH)_2 + 2HCl \to ZnCl_2 + 2H_2O \) (basic behaviour).

Teacher's Note:
1. An amphoteric hydroxide reacts with both an acid and a base.

Question 7: Which substance does NOT react with dilute HCl?
(a) \( ZnCO_3 \)
(b) \( Zn(NO_3)_2 \)
(c) \( Zn(OH)_2 \)
(d) Zn metal
Show Answer & Explanation

Answer: (b) \( Zn(NO_3)_2 \)

Explanation:
1. Zinc carbonate and hydroxide react with acid, zinc metal liberates H2, but zinc nitrate has no reaction with dilute HCl.

Teacher's Note:
1. There is no gas, precipitate or weak electrolyte formed.

Question 8: Which of the following is NOT oxidised by acidified \( K_2Cr_2O_7 \)?
(a) KF (aq)
(b) KCl (aq)
(c) KBr (aq)
(d) KI (aq)
Show Answer & Explanation

Answer: (a) KF (aq)

Explanation:
1. Dichromate oxidises I-, Br- and (on heating with conc. acid) Cl-, but never fluoride.

Teacher's Note:
1. Fluoride is the weakest reducing halide ion.

Question 9: The correct increasing order of ionic radius of \( Ce^{3+} \), \( La^{3+} \), \( Pm^{3+} \) and \( Yb^{3+} \) is
(a) \( La^{3+} < Ce^{3+} < Pm^{3+} < Yb^{3+} \)
(b) \( Ce^{3+} < Yb^{3+} < Pm^{3+} < La^{3+} \)
(c) \( Pm^{3+} < La^{3+} < Ce^{3+} < Yb^{3+} \)
(d) \( Yb^{3+} < Pm^{3+} < Ce^{3+} < La^{3+} \)
Show Answer & Explanation

Answer: (d) \( Yb^{3+} < Pm^{3+} < Ce^{3+} < La^{3+} \)

Explanation:
1. Ionic radii decrease steadily from La to Lu (lanthanoid contraction).
2. Order of atomic number: La (57) < Ce (58) < Pm (61) < Yb (70), so radii: La > Ce > Pm > Yb.

Teacher's Note:
1. Higher atomic number means smaller Ln3+ in the series.

Question 10: V, Cr, Mn and Fe have atomic numbers 23, 24, 25 and 26. Which has the highest second ionisation enthalpy?
(a) Mn
(b) Fe
(c) Cr
(d) V
Show Answer & Explanation

Answer: (c) Cr

Explanation:
1. Removing the second electron from Cr+ (\( 3d^5 \)) breaks the stable half filled \( d^5 \) configuration, so it needs the most energy.

Teacher's Note:
1. Cr and Cu have unusually high second ionisation enthalpies.

Question 11: What happens when potassium chromate solution is treated with excess dilute nitric acid?
(a) \( Cr^{3+} \) and \( Cr_2O_7^{2-} \) are formed
(b) \( Cr_2O_7^{2-} \) and \( H_2O \) are formed
(c) \( Cr_2O_7^{2-} \) is reduced to Cr(III)
(d) \( Cr_2O_7^{2-} \) is oxidised to Cr(VII)
Show Answer & Explanation

Answer: (b) \( Cr_2O_7^{2-} \) and \( H_2O \) are formed

Explanation:
1. \( 2CrO_4^{2-} + 2H^+ \to Cr_2O_7^{2-} + H_2O \). Nitric acid is not a reductant, so the oxidation state of Cr stays +6.

Teacher's Note:
1. Acidification only changes chromate into dichromate; no redox takes place.

Question 12: The radius of \( La^{3+} \) is 1.06 \( \AA \). The radius of \( Lu^{3+} \) (atomic number 71) is closest to
(a) 0.85 \( \AA \)
(b) 1.6 \( \AA \)
(c) 1.4 \( \AA \)
(d) 1.06 \( \AA \)
Show Answer & Explanation

Answer: (a) 0.85 \( \AA \)

Explanation:
1. Lanthanoid contraction reduces the ionic radius from about 1.06 Angstrom (La3+) to about 0.85 Angstrom (Lu3+).

Teacher's Note:
1. The contraction is caused by poor shielding by 4f electrons.

Question 13: Which statement about cerium (Z = 58) is incorrect?
(a) Ce(IV) acts as an oxidising agent
(b) The +3 state is more stable than the +4 state
(c) The common oxidation states are +3 and +4
(d) The +4 oxidation state of cerium is not known in solutions
Show Answer & Explanation

Answer: (d) The +4 oxidation state of cerium is not known in solutions

Explanation:
1. Ce4+ is known in aqueous solution (e.g. ceric ammonium sulphate, a common oxidant), so the statement that it is not known is wrong.

Teacher's Note:
1. Ce(IV) has the stable noble gas configuration but is a strong oxidant.

Question 14: Excess KI reacts with \( CuSO_4 \) solution and then \( Na_2S_2O_3 \) is added. Which statement is incorrect?
(a) Evolved \( I_2 \) is reduced
(b) \( Na_2S_2O_3 \) is oxidised
(c) \( CuI_2 \) is formed
(d) \( Cu_2I_2 \) is formed
Show Answer & Explanation

Answer: (c) \( CuI_2 \) is formed

Explanation:
1. \( 2Cu^{2+} + 4I^- \to Cu_2I_2 + I_2 \): cuprous iodide forms, not \( CuI_2 \) (which does not exist).
2. \( I_2 + 2S_2O_3^{2-} \to 2I^- + S_4O_6^{2-} \).

Teacher's Note:
1. Cupric iodide cannot exist because Cu2+ oxidises iodide.

Question 15: Calomel \( (Hg_2Cl_2) \) on reaction with \( NH_4OH \) gives
(a) \( NH_2\text{-}Hg\text{-}Hg\text{-}Cl \)
(b) \( HgNH_2Cl \) (with black Hg)
(c) \( Hg_2O \)
(d) HgO
Show Answer & Explanation

Answer: (b) \( HgNH_2Cl \) (with black Hg)

Explanation:
1. \( Hg_2Cl_2 + 2NH_3 \to Hg(NH_2)Cl + Hg + NH_4Cl \). The black deposit of mercury gives the name calomel (beautiful black).

Teacher's Note:
1. Calomel turns black with ammonia.

Question 16: The lanthanoid contraction is responsible for the fact that
(a) Zr and Hf have about the same radius
(b) Zr and Y have about the same radius
(c) Zr and Nb have similar oxidation states
(d) Zr and Zn have similar oxidation states
Show Answer & Explanation

Answer: (a) Zr and Hf have about the same radius

Explanation:
1. The 4f electrons shield poorly, so Hf (after the lanthanoids) has nearly the same size as Zr.
2. This is why Zr and Hf are chemically so similar and hard to separate.

Teacher's Note:
1. Similar radii are also seen for Nb and Ta, Mo and W.

Question 17: Lanthanoid contraction is caused by
(a) the same effective nuclear charge from Ce to Lu
(b) appreciable shielding by 4f electrons
(c) appreciable shielding by 5d electrons
(d) imperfect shielding of outer electrons by 4f electrons from the nuclear charge
Show Answer & Explanation

Answer: (d) imperfect shielding of outer electrons by 4f electrons from the nuclear charge

Explanation:
1. The 4f subshell has diffuse shape and shields poorly, so effective nuclear charge rises along the series, shrinking the size.

Teacher's Note:
1. A nuclear charge increase of 1 per element is not cancelled by an added 4f electron.

Question 18: Identify the incorrect statement.
(a) d-block elements show irregular and erratic chemical properties among themselves
(b) The chemistry of the various lanthanoids is very similar
(c) 4f and 5f orbitals are equally shielded
(d) La and Lu have partially filled d orbitals and no other lanthanoid has partially filled d orbitals
Show Answer & Explanation

Answer: (c) 4f and 5f orbitals are equally shielded

Explanation:
1. 5f orbitals are less buried and are shielded less effectively than 4f orbitals, so the statement is wrong.

Teacher's Note:
1. This is why actinoids show more oxidation states than lanthanoids.

Question 19: Actinoids exhibit more oxidation states than lanthanoids because
(a) 5f orbitals are more buried than 4f orbitals
(b) 5f orbitals extend further from the nucleus than 4f orbitals
(c) actinoids are more reactive
(d) 4f and 5f have similar angular wave functions
Show Answer & Explanation

Answer: (b) 5f orbitals extend further from the nucleus than 4f orbitals

Explanation:
1. 5f electrons are less tightly held, and the 5f, 6d and 7s energies are close, so more electrons take part in bonding.

Teacher's Note:
1. This also explains why actinoid ions are more complexing.

Question 20: Which statement about transition elements is incorrect?
(a) In the highest oxidation states the metal shows basic character and forms cationic complexes
(b) In the highest oxidation states of Sc to Mn all 4s and 3d electrons are used for bonding
(c) Once d5 is exceeded, the tendency to involve all 3d electrons decreases
(d) Zero oxidation state is also shown in complexes
Show Answer & Explanation

Answer: (a) In the highest oxidation states the metal shows basic character and forms cationic complexes

Explanation:
1. In the highest oxidation states transition metals form oxides and oxoanions that are acidic, and they form anionic complexes, for example MnO4- and CrO42-.

Teacher's Note:
1. Acidic character rises with oxidation state.

Question 21: Knowing that lanthanoid chemistry is dominated by the +3 state, which statement is incorrect?
(a) Ionic sizes of Ln(III) decrease with increasing atomic number
(b) Ln(III) hydroxides are mainly basic
(c) Bonding in Ln(III) compounds is predominantly ionic
(d) Ln(III) compounds are generally colourless
Show Answer & Explanation

Answer: (d) Ln(III) compounds are generally colourless

Explanation:
1. Most Ln3+ ions with partly filled 4f orbitals are coloured because of f-f transitions, so the statement that they are generally colourless is wrong.

Teacher's Note:
1. La3+ (f0), Lu3+ (f14) and Ce3+ (f1) are colourless, but most others are coloured.

Question 22: Which statement about lanthanoids is not correct?
(a) Radii decrease gradually with atomic number
(b) All members exhibit the +3 state
(c) Availability of 4f electrons results in +4 compounds for all members
(d) Separation is difficult because of similar properties
Show Answer & Explanation

Answer: (c) Availability of 4f electrons results in +4 compounds for all members

Explanation:
1. Only a few members (Ce, Pr, Tb) show +4 and a few show +2 (Eu, Yb).

Teacher's Note:
1. +3 is the characteristic state of all of them.

Question 23: Which statement about iron is incorrect?
(a) Ferrous compounds are less volatile than ferric compounds
(b) Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds
(c) Ferrous oxide is more basic than ferric oxide
(d) Ferric salts are more covalent than ferrous salts
Show Answer & Explanation

Answer: (b) Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds

Explanation:
1. Fe3+ has a higher charge and smaller size, so it is hydrolysed more readily than Fe2+. The given statement is therefore incorrect.

Teacher's Note:
1. Higher oxidation state means more covalent, more volatile and more easily hydrolysed.

The D and F Block Elements Objective Questions & Solutions for JEE Chemistry

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