Question

how many molecules of water will present in a drop of water weighing 0.018 g?

Answer 1

density of water = 1 g/ml

mass of 0.0018 ml of water = 0.0018×1 = 0.0018 g

molar mass of water = 18 g/mol

number of moles in 0.0018g of water = 0.0018/18 = 10^-4

number of water molecules in 1 mole = 6.022×10²³ molecules

number of water molecules in  mole = 6.022 * 10 ^19 molecules