Calculate the moles of each element:

Assume a 100 g sample of the hydrocarbon.
Mass of Carbon (C) = 83.3 g
Mass of Hydrogen (H) = 16.7 g

Calculate the moles of each element:
Moles of C $= \frac{83.3 \text{ g}}{12 \text{ g/mol}} = 6.9417 \text{ mol}$
Moles of H $= \frac{16.7 \text{ g}}{1 \text{ g/mol}} = 16.7 \text{ mol}$

Divide by the smallest number of moles to find the simplest mole ratio:
Ratio of C $= \frac{6.9417}{6.9417} = 1$
Ratio of H $= \frac{16.7}{6.9417} \approx 2.4057$

To obtain whole numbers, multiply the ratios by a suitable integer. Since $2.4057 \approx 2.4 = \frac{12}{5}$, we multiply both ratios by 5:
C: $1 \times 5 = 5$
H: $2.4057 \times 5 = 12.0285 \approx 12$

The empirical formula is $C_5 H_{12}$.

Empirical formula mass $= (5 \times \text{atomic mass of C}) + (12 \times \text{atomic mass of H})$
Empirical formula mass $= (5 \times 12 \text{ g/mol}) + (12 \times 1 \text{ g/mol})$
Empirical formula mass $= 60 \text{ g/mol} + 12 \text{ g/mol} = 72 \text{ g/mol}$

The question states "the vapor density of the hydrocarbon is 36 gdm$^{-3}$". In chemistry problems, "vapor density" is often used to refer to the relative vapor