Question

a metal salt MX exposed to light split up to form metal m and gas x2 metal M is used in making ornament where as x2 is used in making bleeching powder

Answer 1

the metal is silver Ag
the gas is chlorine Cl
the metal salt is silver chloride AgCl
when this salt is exposed to light decomposition reaction takes place.
eq
AgCl. - Ag + Cl2

Answer 2

MX is AgCl here
as Ag is used to make ornaments and Cl is used as component of bleaching powder