Answer
The speed of sound in air is inversely proportional to the square root of molecular mass of the gas.
The humid air has more water in it. Water {18g/mole] has less mass than major components of air , like nitrogen [28g/mole] and oxygen [32 g/mole] etc. Thus addition of water reduces the overall molecular mass of the gas which increases the speed of the sound.
So, speed of sound increases with humidity.
Work Step by Step
The speed of sound in air is inversely proportional to the square root of molecular mass of the gas.
The humid air has more water in it. Water {18g/mole] has less mass than major components of air , like nitrogen [28g/mole] and oxygen [32 g/mole] etc. Thus addition of water reduces the overall molecular mass of the gas which increases the speed of the sound.
So, speed of sound increases with humidity.
