10g of hydrofluoric acid gas occupies 5.6 litre of volume at STP. If the empirical formula of the gas is HF, then its molecular formula will be (Atomic Mass of F = 19)

Empirical formula of HF:

$\mathrm{Mass} \mathrm{of} \mathrm{H}+\mathrm{Mass} \mathrm{of} \mathrm{F}=19+1=20 \mathrm{g}$

At standard temperature and pressure, the volume of one mole of any gas occupies 22.4 litres. Weight by mass ratio can be provided as:

$$\begin{gathered} \frac{\mathrm{w}}{\mathrm{M}}=\frac{5.6}{22.4} \\ \mathrm{M}=40 \mathrm{g} \end{gathered}$$

$\mathrm{n}=\frac{\mathrm{Molecular} \mathrm{mass}}{\mathrm{Empirical} \mathrm{formula}}=\frac{40 \mathrm{g}}{20 \mathrm{g}}=2$

Molecular formula is calculated as:

$\mathrm{Molecular} \mathrm{formula}=\mathrm{n}\times \mathrm{empirical} \mathrm{formula}=2\times \mathrm{HF}={\mathrm{H}}_2{\mathrm{F}}_2$