1
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 10th January Evening Slot

The electrolytes usually used in the electroplating of gold and silver, respectively are:
A
[Au(CN)2] and [Ag(CN)2]
B
[Au(CN)2] and [Ag(Cl)2]
C
[Au(OH)4] and [Ag(OH)2]
D
[Au(NH3)2] and [Ag(CN)2]

Explanation

[Au(CN)2] and [Ag(CN)2] both are soluble complexes.

[Au(CN)2] ⇌ Au+ + 2CN-

[Ag(CN)2] ⇌ Ag+ + 2CN-

The concentration of produced Au+ ion and Ag+ ion due to ionisation is very less which ensure slow deposition and this slow deposition will generate uniform layer on the substance to be electroplated.
2
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 11th January Morning Slot

Match the ores (column A) with the metals (column B) :

(Column A) ores (Column B) Metals
(I) Siderite (a) Zinc
(II) Kaolinite (b) Copper
(III) Malachite (c) Iron
(IV) Calamine (d) Aluminium
A
(I)-(c); (II)-(d); (III)-(b); (IV)-(a)
B
(I)-(a); (II)-(b); (III)-(c); (IV)-(d)
C
(I)-(b); (II)-(c); (III)-(d); (IV)-(a)
D
(I)-(c); (II)-(d); (III)-(a); (IV)-(b)

Explanation

Siderite : FeCO3

Kaolinite : Al2(OH)4Si2O5

Malachite : CuCO3 .Cu(OH)2

Calamine : ZnCO3
3
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 12th January Morning Slot

In the Hall-Heroult process, aluminium is formed at the cathode. The cathode is made out of -
A
Copper
B
Platinum
C
Carbon
D
Pure aluminium

Explanation

In the Hall-Heroult process the cathode is made of carbon.
4
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 12th January Evening Slot

The pair that does NOT require calcination is -
A
Fe2O3 and CaCO3⋅MgCO3
B
ZnCO3 and CaO
C
ZnO and Fe2O3⋅xH2O
D
ZnO and MgO

Explanation

In calcination, we convert a compound or ore into oxide.

In option (D) you can see there is ZnO and MgO, as they are already in oxide form so no calcination required for then.

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