Thank you for reporting, we will resolve it shortly
Q.
$100 \,mL$ of $PH_3$ when completely decomposed produces phosphorus and hydrogen. The change in volume of the gas is -
$PH_3(g) \to P(s) + 3/2 H_2(g)$
Some Basic Concepts of Chemistry
Solution:
$\underset{\text{2 vol}}{2PH_{3}} \to \underset{\text{3 vol}}{3H_{2}}+2P$
$ 2$ vol of $PH_{3}$ give $3$ vol of $H_{2}$
$\therefore 100\,mL$ of $PH_{3}$ gives $150\,mL$ of $H_{2}$
$\therefore $ Increase in volume $=150\,mL-100\,mL$
$=50\,mL$