Which method/process is used to obtain aluminium from pure alumina?

State whether the following statement is true or false:
The elements or compounds,which occur naturally in the earth's crust,are known as minerals.

State reasons for the following:
$(i)$ Metals are good conductors of heat.
$(ii)$ Addition of some silver to pure gold for making ornaments.
$(iii)$ Inability of non-metals to displace hydrogen from dilute sulphuric acid.

What type of oxide is $H_{2}O$?

Which of the following acids is called 'the king of chemicals'?

State whether the following statement is true or false:
Copper does not burn in air, but the hot metal is coated with a black-coloured layer of copper $(II)$ oxide.