Chemistry - Ideal Gas Question with Solution | TestHub

Moles of $P$ = 3.1/31 = 0.10. Moles of $C{l}_2$ = 12.78/71 = 0.18.

Let x mol $PC{l}_3$ and y mol $PC{l}_5$: x + y = 0.10 (phosphorus).

Chlorine: 1.5x + 2.5y = 0.18 (each $PC{l}_3$ needs 1.5 $C{l}_2$, each $PC{l}_5$ needs 2.5 $C{l}_2$).

Substituting x = 0.10 - y: 0.15 + y = 0.18, so y = 0.03 and x = 0.07.

Mole fraction of $PC{l}_5$ = 0.03/0.10 = 0.30.

Answer: (B).