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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ce209

A gas $A$ dissociates as $A (g) n B (g)$ ( $n \geq 2$ integer) with degree of dissociation $α$ , starting from 1 mol at constant $T$ and $P$ . $D$ is the calculated vapour density of undissociated $A$ and $d$ that of the mixture. Select the correct statements.

A $d = D [1 + (n - 1) α]$
B $α = \frac{D - d}{( n - 1 ) d}$
CIf $n = 3$ and $d = D /2$ , then $α = 0.5$
DOn complete dissociation, $d = D / n$

Answer: B, C, D

Total moles are

1 - α + n α = 1 + (n - 1) α

, and

d = D / [1 + (n - 1) α]

, so (A) is false and (B) true. For

n = 3

,

d = D /2

:

2 = 1 + 2 α

,

α = 0.5

(C true). At

α = 1

,

d = D / n

(D true).

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