A sample of water gas contains 42% by volume of carbon monoxide. If the total pressure is 760 mm. the partial pressure of carbon monoxide in mm Hg is

Let us assume mole percentage is equal to volume percentage.

Total moles=100

Moles of water=100-42=58

${\mathrm{x}}_{\mathrm{CO}}=\frac{42}{42+58}$

${\mathrm{x}}_{\mathrm{CO}}=\frac{42}{100}$

${\mathrm{x}}_{\mathrm{CO}}=\frac{42}{42+58}$

${\mathrm{P}}_{\mathrm{CO}}=\frac{42}{42+58}\times 760$

${\mathrm{P}}_{\mathrm{CO}}$=319.2 mm

Therefore, the required answer is B.