Convert into mole
20g of water

20 g of water into mole

molar mass of water($H_{2}O$) = 2 x H + O
= 2 x 1g/mol + 16g/mol
= 18 g/mol

Given mass = 20 g
molar mass = 18g/mol

number of moles = given mass/ molar mass
= 20g /(18 g/mol)
= 1.11 mol
so 20 g of water = 1.11 mol of water