The addition of a nitrite solution to a solution of KI, followed by acidification with acetic acid, results in the liberation of iodine, which may by identified by following:

Here, the reaction is,

${\mathrm{I}}^{-}+{\mathrm{NO}}_2^{-}\stackrel{{\mathrm{H}}^{+}}{\to }\underset{\text{identifry }}{\underbrace{{\mathrm{I}}_2\uparrow }}$

The colors obtained as,

Starch paste =$={\mathrm{I}}_2:$ Deep colour

Chloroform layer = ${\mathrm{I}}_2$: violet

${\mathrm{CS}}_2$ layer = $={\mathrm{I}}_2$: violet colour

Thus, option a, b and c are correct.