What do you understand by calcination and roasting? What are the differences between them?

Give an example to illustrate the following terms used in metallurgy.

i) Slag 

ii) gangue

iii) roasting

iv) flux

Give reason for the following: $\mathrm{Na}, \mathrm{K}, \mathrm{Ca}$ metals form hydrides by combination with hydrogen gas, but most other metals do not.

Discuss briefly the following process used in metallurgy: Electrolytic refining