"Metals are usually not found as nitrates in their ores". Out of the following two (I and II) reasons which is/are true for the above observation? 

Roasting of sulphides gives the gas X as a by-product. This is a colourless gas with a choking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic and  acts as an oxidizing agent and its acid has never been isolated. The gas X is:

1. SO₂

2. CO₂

3. SO₃

4. H₂S

Aluminium is extracted from alumina Al₂O₃ by electrolysis of a molten mixture of:

1. ${\mathrm{Al}}_2{\mathrm{O}}_3+\mathrm{HF}+{\mathrm{NaAlF}}_4$

2. ${\mathrm{Al}}_2{\mathrm{O}}_3+{\mathrm{CaF}}_2+{\mathrm{NaAlF}}_4$

3. ${\mathrm{Al}}_2{\mathrm{O}}_3+{\mathrm{Na}}_3{\mathrm{AlF}}_6+{\mathrm{CaF}}_2$

4. ${\mathrm{Al}}_2{\mathrm{O}}_3+\mathrm{KF}+{\mathrm{Na}}_3{\mathrm{AlF}}_6$

Which one of the following is a mineral of iron?

1. Malachite

2. Cassiterite

3. Pyrolusite

4. Magnetite

An interstitial compound among the following is:

1. Invar

2. Steel

3. Bell metal

4. Bronze

Which of the following elements is present as an impurity to the maximum extent in the pig Iron?
1. Carbon
2. Silicon
3. Phosphorus
4. Manganese

The following reactions take place in the blast furnace in the preparation of impure iron.
Identify the reaction pertaining to the formation of the slag.

1. 2C(s) + O₂(g) → 2CO (g)
2. Fe₂O₃(s) + 3CO (g) → 2Fe(l) + 3CO₂(g)
3. CaCO₃(s) → CaO(s) + CO₂(g)
4. CaO(s) + SiO₂(s) → CaSiO₃(s)

Sulphide ores of metals are usually concentrated by the froth flotation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

1. Argentite

2. Galena

3. Copper pyrite

4. Sphalerite