Question

60% relative humidity is how many kg of mositure in air

Answer 1

60% relative humidity

It means out of 100 molecules of air 60 molecules are water.

Concentration of Air is not persistent everywhere one area may have more concentration another may have less. So i cant tell the weight of moisture in terms of kg as you have not specified how much amount of air you are talking about.

Let's say there is 100kg of air because 60% of it is moisture we can say moisture content is 60kg.

Hope this helps☺