# The correct statement is :

Question:

The correct statement is :

1. leaching of bauxite using concentrated $\mathrm{NaOH}$ solution gives sodium aluminate and sodium silicate.

2. the Hall-Heroult process is used for the production of aluminium and iron.

3. pig iron is obtained from cast iron.

4.  the blistered appearance of copper during the metallurgical process is due to the evolution of $\mathrm{CO}_{2}$.

Correct Option: 1

Solution:

During metallurgy of aluminium, when bauxite (powdered ore) is treated with $\mathrm{NaOH}$ (conc), sodium aluminate $\left(\mathrm{Na}\left[\mathrm{Al}(\mathrm{OH})_{4}\right]\right)$ is formed and impurity $\left(\mathrm{SiO}_{2}\right)$ present in bauxite dissolves by forming sodium silicate $\left(\mathrm{Na}_{2} \mathrm{SiO}_{3}\right)$

$\mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s})+2 \mathrm{NaOH}(\mathrm{aq})+3 \mathrm{H}_{3} \mathrm{O}(\mathrm{l}) \underset{2 \mathrm{Na}}{\rightarrow}\left[\mathrm{Al}(\mathrm{OH})_{4}\right](\mathrm{aq})$

Cast iron is obtained from pig iron.

Blister of copper is due to evolution of $\mathrm{SO}_{2}$.

Hall Heroult process is used for the production of aluminium.