If a sample of air contains 1 g/kg of water vapor and has a relative humidity of 25 percent at -5 degrees celsius how much water vapor does it need to contain to be saturated?
a) 2 g/kg
b) 1 g/kg
c) 4 g/kg
d) 3 g/kg

Option C

Explanation:

As we know that

Relative humidity (RH) is defined as the ratio of amount of water vapor present in a given sample of air to the maximum amount of water that can be  absorbed by the same sample of air to attain saturation  at a particular temperature .

Thus,

Where X represents the current amount of water vapor present in a given sample of air

and Y represents the maximum amount of water that can be  absorbed by the same sample of air to attain saturation  at a particular temperature

Substituting the given values in above equation we get -

Hence, option C is the correct answer