Sodium salt $\left(\mathrm{A}\right)$ of a dibasic acid $\stackrel{\mathrm{HCl}}{\to }\mathrm{gas} \left(\mathrm{B}\right)$ and clear solution of gas $\left(\mathrm{B}\right)$ turns ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ to green and also lime water milky. Identify atomicity of gas $\left(\mathrm{B}\right)$

An aqueous solution of a gas $\left(\mathrm{X}\right)$ gives the following reactions:

(i) It decolourises an acidified ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ solution.

(ii) On boiling with ${\mathrm{H}}_2{\mathrm{O}}_2$ and cooling it and then adding an aqueous of ${\mathrm{BaCl}}_2$ in dil. $\mathrm{HCl}$, is produced.

(iii) On passing ${\mathrm{H}}_2\mathrm{S}$ in the solution, white turbidity is formed. Identify the molecular mass of gas $\left(\mathrm{X}\right)$?

An aqueous solution of a gas $\left(\mathrm{X}\right)$ shows the following reactions.

(i) It turns red litmus blue

(ii) When added in excess to a ${\mathrm{CuSO}}_4$ solution, a deep blue colour is obtained

(iii) On addition of ${\mathrm{FeCl}}_3$ solution a brown precipitate soluble in dilute ${\mathrm{HNO}}_3$ is obtained.

Identify the molecular mass of gas $\left(\mathrm{X}\right)$?