The vapour density of a mixture consisting of NO₂ and N₂O₄ is 38.3 at 275 K. The number of mole of N₂O₄ in 100 g of the mixture is

Vapour density of NO₂​+N_2​O₄​ = 38.3

Mass of 1 mole of mixture = vapour density × 2 = 76.6

Number of moles in the mixture =$\frac{100}{76.6}=1.305$

Let the mass of NO₂​ be x

$\frac{x}{46}+\frac{100-x}{92}=1.305$​

x=20.1
Number of moles of NO₂​ present in 100gm of the mixture =$\frac{20.1}{46}=0.437$