Em tham khảo nha:
\(\begin{array}{l}
a)\\
CTHH\,:X{H_4}\\
{M_{X{H_4}}} = {M_O} = 16\,dvC\\
\Rightarrow {M_X} + 4{M_H} = 16 \Rightarrow {M_X} = 16 - 1 \times 4 = 12\,dvC\\
\Rightarrow X:Cacbon(C)\\
b)\\
\% {m_C} = \dfrac{{12}}{{16}} \times 100\% = 75\% \\
\% {m_H} = 100 - 75 = 25\%
\end{array}\)