# 11.22.    Give reasons :  (ii) A mixture of dilute $N\! aO\! H$ and aluminium pieces is used to open drain.

When the mixture of dilute $N\! aO\! H$ and aluminium pieces reacts, they formed sodium tetrahydroxy aluminate (III)and dihydrogen gas. To open the drains, we use the pressure produced by the hydrogen gas.
$2Al+NaOH+6H_{2}O\rightarrow 2Na+[Al(OH)_{4}]^{-}+3H_{2}$