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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3mc108

A mixture of $CO$ and $CO X_{2}$ ( $28$ and $44 g/mol$ ) contains $30%$ carbon by mass ( $C = 12$ ). Choose the correct statement(s).

AThe mole fraction of $CO$ is $0.25$ .
BThe average molar mass is $40 g/mol$ .
CThe vapour density is $40$ .
DThe mass percent of $CO$ is $25%$ .

Answer: A, B

Carbon per mole of mixture = 12 g (each molecule has one C atom). 12/M = 0.30 gives M = 40, i.e. 28x + 44(1-x) = 40, so x = 0.25 (A, B true). Vapour density = 40/2 = 20, not 40 (C false). Mass % of

CO

= 0.25 x 28/40 x 100 = 17.5%, not 25% (D false).

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