An alkane has a $\mathrm{C}/\mathrm{H}\text{-ratio }$ (by mass) of 5.1428. Its molecular formula is

The ratio of C/H in an alkane is 5.1428

Alkanes have General formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$

The mass ratio of $\frac{\mathrm{C}}{\mathrm{H}}\text{ is }\frac{12\mathrm{n}}{2\mathrm{n}+2}\text{ or }\frac{6\mathrm{n}}{\mathrm{n}+1}=5.1428$

$\begin{array}{l}6\mathrm{n}=5.1428\mathrm{n}+5.1428\to 0.8572\mathrm{n}=5.1428\\ \mathrm{n}=\frac{5.1428}{0.8572}=6\end{array}$

molecular formula = ${\mathrm{C}}_6{\mathrm{H}}_{2\mathrm{n}+2}={\mathrm{C}}_6{\mathrm{H}}_{14}.$