Carbon combines with hydrogen to form three compounds, $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$. The percentage of hydrogen in $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$ are $25\%, 14.3\%$ and $7.7\%$ respectively. Find the empirical formula of the compound.

A hydrated salt of iron$\left(\mathrm{II}\right)$ sulphate weighing $2 \mathrm{g}$, contains $0.9065 \mathrm{g}$ of water of crystallisation. Find the formula of the hydrated salt.

(Molar mass of ${\mathrm{H}}_2\mathrm{O}=18,{\mathrm{FeSO}}_4=152$)

$1.763 \mathrm{g}$ of hydrated ${\mathrm{BaCl}}_2$ was heated to dryness. The anhydrous salt remained was $1.505 \mathrm{g}$. What is the formula of the hydrate?

(Molar mass of ${\mathrm{H}}_2\mathrm{O}=18, {\mathrm{BaCl}}_2=208$)

$9$ volumes of a gaseous mixture consisting of a gaseous organic compound $\mathrm{A}$ and just sufficient amount of  oxygen required for complete combustion yielded on burning $4$ volumes of ${\mathrm{CO}}_2,$ $6$ volumes of water vapour and $2$ volumes of ${\mathrm{N}}_2$, all volumes measured at the same temperature and pressure. If the compound has only$\mathrm{C}, \mathrm{H}$ and $\mathrm{N}$, how many volumes of ${\mathrm{O}}_2$ are required for complete combustion?

Nine volumes of a gaseous mixture consisting of a gaseous organic compound $\mathrm{A}$ and just sufficient amount of ${\mathrm{O}}_2$ required for complete combustion yielded on burning four volumes of ${\mathrm{CO}}_2, 6$ $\mathrm{volumes}$ of water vapour and two volumes of ${\mathrm{N}}_2$ all volumes measured at the same temperature and pressure. If the compound has only$\mathrm{C}, \mathrm{H}$ and $\mathrm{N}$, what is the molecular formula of the compound $\mathrm{A}$?