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

The correct statement among the following is:  

\((i) Zr + 2I_2 \xrightarrow{870K} ZrI_4 \xrightarrow{2075K} Zr + 2I_2 \)
\((ii) Ni + 4CO \xrightarrow{330K} Ni(CO)_4 \xrightarrow{450K} \underset{(pure)}{Ni} + 4CO \)

The processes (ii) and (i) above, respectively, are  : 

1. Mond's process; Van Arkel process

2. Van Arkel process; Mond's process

3. Goldschmidt process; Mond's process

4. Mond's process; Goldschmidt process

Which metal can be purified by zone refining?

1. Ni

2. Zr

3. In

4. Fe

The chemical composition of "slag" formed during the smelting process in the extraction of copper is:

1. Cu₂ + FeS                                    

2. FeSiO₃

3. CuFeS                                         

4. Cu₂S + FeO

The correct statement among the following is: 

The fundamental principle of froth flotation process is:

NaCN is a depressant that is used: 

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?