Oxygen is collected over water at $2 5^{\circ} C$ when the barometric pressure is $760 mm Hg$ and the aqueous tension is $24 mm Hg$ . Which statements are correct?

AThe partial pressure of dry $O X_{2}$ is $736 mm Hg$
BThe mole fraction of water vapour in the collected gas is $24/760$
CIf the gas were collected over mercury instead, the same volume would contain more $O X_{2}$
DDrying the collected gas at constant $T$ and $P$ would increase its volume

Answer: A, B, C

Dalton's law:

p_{O X_{2}} = 760 - 24 = 736 mm Hg

(A) and

x_{H X_{2} O} = 24/760

(B). Over mercury there is no water vapour, so

O X_{2}

fills the whole

760 mm

and the same volume holds more

O X_{2}

(C). Removing water vapour at the same

T

and

P

reduces the moles of gas and hence the volume (D wrong).