The aqueous solution of a inorganic compound $\left(\mathrm{X}\right)$ yielded a white precipitate when treated with dil ${\mathrm{HNO}}_3$ and ${\mathrm{AgNO}}_3$. Another sample of the solution of $\left(\mathrm{X}\right)$ when treated with $\mathrm{NaOH}$ gave a white precipitate first which dissolved in excess of $\mathrm{NaOH}$ yielding a colorless solution. When ${\mathrm{H}}_2\mathrm{S}$ gas was passed through that solution a white precipitate was obtained. Identify the atomic number of cation which is present in compound $\left(\mathrm{X}\right)$?

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 $\left(\mathrm{X}\right)$?

A unknown inorganic compound $\left(\mathrm{X}\right)$ gave the following reaction:

(i) on heating $\text{'}\mathrm{X}\text{'}$ gave a residue, oxygen and oxide of nitrogen.

(ii) Addition of acetic acid and ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ to its aqueous solution give a yellow precipitate.

(iii) Addition of $\mathrm{NaOH}$ to its aqueous solution first forms a white precipitate. Dissolve in the excess of the reagent.