What are the answers for these two questions?

This question looks more like a reasoning based on theory , so will answer it in an analytic method.

Here, we see that, the gas produced X₂  from the salt MX is involved in formation of bleaching powder, so, first of all we consider the formation of bleaching powder Ca(OCl)Cl or CaOCl₂ involves;

Ca (OH)₂ (slaked lime or calcium hydroxide)+ Cl₂ (chlorine gas) ---> Ca (OCl)Cl + H₂O

Further, the metal M is used in ornaments so ,it may be Au(gold), Ag(silver), Platinum(Pt)etc.

But, the metal salt is MX (Metal chloride) and as Chlorine is monovalent  with -1 oxidation state so the metal should also have +1 Oxidation state to form MX salt.

Hence, the metal with +1 oxidation state is silver (Ag) which forms silver chloride with Cl₂ gas as AgCl (MX salt), and it is also used in black and white photography.

Thus,

1. Metal M is silver (ag)

2. the gas X₂ is chlorine Cl₂ 

3. The metal salt (MX) is silver chloride or AgCl.

4.Chemical reaction  of decomposition of AgCl is on exposure to light is known as photolysis