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Average molar mass of mixtures, vapour density
JEE Main level
Single correct option
Difficulty 2 of 3
mc096
Dry air is taken as
80%
N
X
2
and
20%
O
X
2
by volume (
N
X
2
=
28
,
O
X
2
=
32
g/mol). The vapour density of air (relative to hydrogen) is
A
28.8
B
14.4
C
15.0
D
15.6
Answer: B
Volume % equals mole %. Average molar mass = 0.8 x 28 + 0.2 x 32 = 28.8 g/mol. Vapour density = 28.8/2 = 14.4.
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