A sample of air contains only `N_(2), O_(2)` and `H_(2)`. It is saturated with water vapours and the total pressure is 640 torr. The vapour pressure of water is 40 torr and the molar ratio of `N_(2) : O_(2)` is `3: 1`. The partial pressure of `N_2` in the sample is:

Options

A. 480 torr
B. 600 torr
C. 525 torr
D. 450 torr

Answer

D

Explanation

Pressure of dry air = `P_("moist air") - P_("water vapours") = 640 – 40 = 600` torr.
Partial pressure = mole fraction `xx P_(T)`
`therefore` Partial pressure of `N_2` and `O_2` are also in the ratio of `3:1`.
Partial pressure of `N_(2) = (600 xx 3)/(3 + 1) = 450` torr.