JEE Chemistry The D and F Block Elements MCQs Set 15

Answer: (a) 50 mL of 0.1 M \( \ce{C2H2O4} \)

Explanation:
1. Moles of \( \ce{MnO4^-} \) = 20 x 0.1 = 2 mmol.
2. From the equation 2 mol need 5 mol of oxalic acid, so 5 mmol is required.
3. 5 mmol at 0.1 M is 50 mL.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) 31.6

Explanation:
1. M/5 = 158/5 = 31.6.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (c) Potassium permanganate is a weaker oxidising substance than potassium dichromate

Explanation:
1. In acid, \( E^\circ(MnO_4^-/Mn^{2+}) = 1.51 \) V is higher than \( E^\circ(Cr_2O_7^{2-}/Cr^{3+}) = 1.33 \) V.
2. So permanganate is the stronger oxidant and the 'weaker oxidising substance' claim is wrong.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (d) \( \ce{HgCl2} \)

Explanation:
1. Mercuric chloride, \( \ce{HgCl2} \), sublimes on heating and is highly poisonous.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (c) \( \ce{Ag2O} \)

Explanation:
1. \( \ce{Ag2O} \) is a mild oxidant, used in Tollens-type oxidations; the others are strong oxidants.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (b) 49

Explanation:
1. Equivalent weight = 294/6 = 49.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) paramagnetic

Explanation:
1. Copper(II) sulphate is isomorphic with zinc sulphate. \( \ce{Cu^{2+}} \) is 3d⁹ with one unpaired electron, so the salt is paramagnetic.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) \( \ce{H2SO4} \)

Explanation:
1. \( \ce{V2O5} \) catalyses the oxidation of \( \ce{SO2} \) to \( \ce{SO3} \) in the contact process.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (c) 7 to 2

Explanation:
1. Permanganate (+7) is reduced to \( \ce{Mn^{2+}} \) (+2) in acid.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) \( \ce{K2HgI4 + KOH} \)

Explanation:
1. Nessler's reagent is an alkaline solution of potassium tetraiodomercurate(II).

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (d) \( \ce{N2} \)

Explanation:
1. \( \ce{(NH4)2Cr2O7 -> N2 + Cr2O3 + 4H2O} \).

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

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

Explanation:
1. \( \ce{Cr2O7^{2-} + 3SO3^{2-} + 8H^+ -> 2Cr^{3+} + 3SO4^{2-} + 4H2O} \).

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (b) \( \ce{IO3^-} \)

Explanation:
1. \( \ce{2MnO4^- + I^- + H2O -> 2MnO2 + IO3^- + 2OH^-} \).
2. In alkaline medium iodide is oxidised all the way to iodate.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (d) It reacts with KCl to give \( \ce{Cu2Cl2} \)

Explanation:
1. Copper sulphate does not react with KCl to give \( \ce{Cu2Cl2} \), since chloride is not a strong enough reducing agent.
2. Iodide reduces it to CuI and \( \ce{I2} \); with glucose in alkali it gives red \( \ce{Cu2O} \).

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (c) Mohr's salt

Explanation:
1. Mohr's salt contains \( \ce{Fe^{2+}} \), which reduces purple permanganate to colourless \( \ce{Mn^{2+}} \).

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (b) \( \ce{ZnO} \)

Explanation:
1. ZnO is white at room temperature and turns yellow when hot, reverting to white on cooling.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (b) alloys which contain mercury as one of the constituents

Explanation:
1. An amalgam is an alloy in which one component is mercury.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) a complexing agent

Explanation:
1. Hypo dissolves unreacted AgBr by forming the soluble complex \( \ce{[Ag(S2O3)2]^{3-}} \).

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (b) mercurous chloride

Explanation:
1. Mercurous chloride (calomel) sublimes on heating. (It also disproportionates, but sublimation is the characteristic observation.)

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) \( \ce{Fe2(SO4)3} \)

Explanation:
1. A paramagnetic substance is drawn into the field and appears heavier. \( \ce{Fe^{3+}} \) (d⁵) is paramagnetic; \( \ce{Ti^{4+}} \), \( \ce{Mn^{7+}} \) and \( \ce{Sc^{3+}} \) are d⁰.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) \( \ce{TiF6^{2-}} \) and \( \ce{Cu2Cl2} \)

Explanation:
1. Ti(IV) is d⁰ and Cu(I) is d¹⁰, so both are colourless.
2. Co(III) is d⁶ and Ni(II) is d⁸ and coloured.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (a) \( \ce{Cr2O3} \)

Explanation:
1. Chromium(III) oxide gives glass a green colour.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (b) copper oxide

Explanation:
1. \( \ce{2Cu(NO3)2 -> 2CuO + 4NO2 + O2} \).

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (b) cuprous iodide is precipitated with liberation of iodine

Explanation:
1. \( \ce{2Cu^{2+} + 4I^- -> Cu2I2 + I2} \).
2. White CuI is precipitated and iodine is liberated.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (d) \( \ce{CrO2Cl2} \)

Explanation:
1. This is the chromyl chloride test: red-brown vapours of \( \ce{CrO2Cl2} \) are formed.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (d) decomposed in sunlight

Explanation:
1. Light decomposes silver nitrate to silver, nitrogen dioxide and oxygen, so it is stored in amber bottles.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.

Answer: (c) silver

Explanation:
1. Silver chloride is a white precipitate soluble in dilute ammonia.

Teacher's Note:
1. Link each compound to its colour, oxidation state and reaction medium; these facts are asked repeatedly.
2. For redox questions, count the electrons exchanged per formula unit before choosing an option.