A mixture of $O X_{2}$ and $O X_{3}$ has an average molar mass of $38.4 g mo l^{- 1}$ (O = 16). The mass percentage of $O X_{3}$ in the mixture is

A $40%$
B $60%$
C $75%$
D $50%$

Answer: D

Let the mole fraction of O3 be x: 48x + 32(1 - x) = 38.4, so x = 0.40. In 1 mol mixture the mass of O3 = 0.40 x 48 = 19.2 g out of 38.4 g, i.e. 50% by mass (the 40% is the mole percentage).

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A mixture of OX2​ and OX3​ has an average molar mass of 38.4 g mol−1 (O = 16). The mass percentage of OX3​ in the mixture is

Answer: D

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A mixture of $O X_{2}$ and $O X_{3}$ has an average molar mass of $38.4 g mo l^{- 1}$ (O = 16). The mass percentage of $O X_{3}$ in the mixture is