$20 mL$ of $NH X_{3}$ is completely decomposed into $N X_{2}$ and $H X_{2}$ by electric sparks in a eudiometer. The volume of the gaseous mixture after decomposition (same $T$ and $P$ ) is

Answer: A

2 NH X_{3} N X_{2} + 3 H X_{2}

20 mL

NH X_{3}

gives

10 mL

N X_{2}

and

30 mL

H X_{2}

, total

40 mL

: the volume doubles.