Question

The mass ratio of carbon to hydrogen in methane is 3:1. How much amount of hydrogen is required to react with 36 g of carbon to form methane?

Answer 1

The chemical formula of methane is $C{H}_4$. The carbon to hydrogen mass ratio in it is $3:1$.
3 g of carbon requires 1 gram of hydrogen.
So, 36 g of carbon requires
=$\frac{36}{3}\times 1=12\text{g}$ of hydrogen.