Which of the following ions can be separated by using dilute $\mathrm{HCl}$?

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 $\left(\mathrm{X}\right)$?

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.

An inorganic compound $\left(\mathrm{X}\right)$ gives brick red flame on performing the flame test. This also give the following tests:

(i) Smell of chlorine when placed in moist air.

(ii) If $\mathrm{KI}$ & ${\mathrm{CH}}_3\mathrm{COOH}$ are added to its suspension in water, a brown colour is obtained. Identify $\left(\mathrm{X}\right)$ and write down equations for reactions at step (i) and (ii).

Two solid laboratory reagents $\left(\mathrm{A}\right)$ and $\left(\mathrm{B}\right)$ give following reactions:

Compound: $\left(\mathrm{A}\right)$

(i) On strongly heating it gives two oxides of sulphur.

(ii) On adding aqueous $\mathrm{NaOH}$ solution to its aqueous solution, a dirty green precipitate is obtained which starts turning brown on exposure to air.

Compound: $\left(\mathrm{B}\right)$

(iii) It imparts green colour to flame.

(iv) Its solution doesn't give precipitate on passing ${\mathrm{H}}_2\mathrm{S}$

(v) When it is heated with ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ & conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$, a red gas is evolved. The gas when passed in aqueous $\mathrm{NaOH}$ solution turns it yellow.

Identify $\left(\mathrm{A}\right)$ to $\left(\mathrm{B}\right)$ and give chemical reactions.