$A + H_2O \to B + HCl$
$B + H_2O \to C + HCl$
Compound $(A), (B)$ and $(C)$ will be respectively

Basicity of phosphinic acid is

$A$ tetra-atomic molecule $(A)$ on reaction with nitrogen $(I)$ oxide,produces two substances $(B)$ and $(C).$ $(B)$ is a dehydrating agent in its monomeric form while substance $(C)$ is a diatomic gas which shows almost inert behaviour. The substances $(A)$,$(B)$,and $(C)$ respectively will be

When calomel reacts with $NH_4OH$ solution,the compound formed is

Pure $HNO_3$ is colorless. However,it turns slightly brown when exposed to light due to its decomposition into $.....$.

Write four main properties of $p$-block elements.