Question

How many grams of oxygen $\left(O_2\right)$ are required to completely react with $0.20\text{g}$ of hydrogen $\left(H_2\right)$ to yield water $\left(H_{2}O\right)$? (molar mass $H_2=2\text{g/mol},O_2=32\text{g/mol}$)

Answer 1

According to the reaction:
$2H_2\text{(g)}+O_2\text{(g)}\to 2H_{2}O\text{(l)}$
$4\text{g}$ of hydrogen reacts with $32\text{g}$ of oxygen.
So, $0.2\text{g}$ of hydrogen reacts with $(\frac{32}{4}\times 0.2)=1.6\text{g}$ of oxygen