A vessel contains a mixture of equal weights of oxygen and SO₂ at a pressure of 600mm of Hg. The partial pressure of oxygen in mm is

Partial pressure of oxygen is equal to product of total pressure and mole fraction of oxygen.

Mole fraction of oxygen=$\frac{\mathrm{M}}{32}$

Mole fraction of Sulphur dioxide=$\frac{\mathrm{M}}{64}$

Total mole fraction=

$\frac{\mathrm{M}}{32}+\frac{\mathrm{M}}{64}$$=\frac{3\mathrm{M}}{64}$

Mole fraction of oxygen=$\frac{\mathrm{M}/32}{3\mathrm{M}/64}$

Mole fraction=⅔

Now according to Dalton's law

=600×2/3

=400 mm of Hg

Hence the correct answer is C