Question

how many molecules are present in one ml of water vapours at STP

Answer 1

water vapour= H2O =18g
if 18g of H2O are present in 1000mL
then, 1mL of H2O have Xg of water vapour

therefore....X= 1000×1×22.4/18

where at stp =22.4L
ans. is 12.4