Answer:
[tex]\boxed{\text{17.76 \% by mass}}[/tex]
Explanation:
[tex]\text{The mass of one molecule of NH$_{3}$ is:}\\\text{14.01 u N + 3.024 u H = 17.034 u}\\\\\text{mass $\%$ H} =\dfrac{3.024}{17.034} \times 100 \%} =\textbf{17.76 \%}\\\\\text{Ammonia contains }\boxed{\textbf{17.76 \% H by mass}}[/tex]
