NaCN is a depressant that is used: 

1.	To Separate PbS from ZnS by forming a complex with PbS.
2.	To Separate PbS from ZnS by forming a complex with ZnS.
3.	To Form froth.
4.	As a collector.

Ellingham's diagram for the formation of ${\mathrm{CO}}_2$ is a straight line in the given graph. This is due to:

1. Increase in entropy during ${\mathrm{CO}}_2$ formation.

2. Decrease in entropy during ${\mathrm{CO}}_2$ formation.

3. Entropy remains constant during ${\mathrm{CO}}_2$ formation.

4. Can not be predicted.

Why is roasting important in the iron metallurgy process?  

The fundamental principle of froth flotation process is:

4M + 8CN^- + 2H₂O + O₂$\to$ 4[M(CN)₂]^- + 4OH^-

2[M(CN)₂]^- + Zn$\to$[Zn(CN)₄]^2- + 2M

The metal M in above-mentioned reaction is:

1. Nickel

2. Silver

3. Copper

4. Mercury

The extraction of gold and silver involves leaching with CN^- ion. Silver is later recovered by:

1. Liquation

2. Distillation

3. Zone refining

4. Displacement with Zn

The substance that acts as a collector in the froth flotation method is:

1. Sodium xenate.           

2. Sodium pyrophosphate.

3. Sodium nitroprusside.

4. Sodium ethyl xanthate. 

Which of the following is an incorrect match?

1. Kaolinite - Al₂(OH)₄Si₂O₅

2. Cuprite - Cu₂O

3. Siderite - FeCO₃

4. Calamine - ZnSO₄

Among the following a non-oxide ore is:

1. Malachite

2. Cuprite

3. Zincite

4. Bauxite

2MS + 3O₂ → 2MO + 2SO₂
2MO + MS → 3M + SO₂

The metal M in above-mentioned reaction is:

1. Mg

2. Pb

3. Sn

4. Fe