On the surface of polar stratospheric clouds, hydrolysis of chlorine nitrate gives $\mathrm{A}$ and $\mathrm{B}$ while its reaction with $\mathrm{HCl}$ produces $\mathrm{B}$ and $\mathrm{C}$. $\mathrm{A}.\mathrm{B}$ and $\mathrm{C}$ are, respectively

In winter, special type of clouds called polar stratospheric clouds are formed over Antarctica.These polar stratospheric clouds provide surface on which chlorine nitrate formed gets hydrolysed to form hypochlorous acid.It also reacts with hydrogen chloride produced to give molecular chlorine

The reactions are:

${\mathrm{ClONO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)\to \mathrm{HOCl}\left(\mathrm{g}\right)+{\mathrm{HNO}}_3\left(\mathrm{g}\right)$

${\mathrm{ClONO}}_2\left(\mathrm{g}\right)+\mathrm{HCl}\left(\mathrm{g}\right)\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+{\mathrm{HNO}}_3\left(\mathrm{g}\right)$

Hence, A, B and C are $\mathrm{HOCl},{\mathrm{HNO}}_3,{\mathrm{Cl}}_2$