The molecular weight of water is 18.01528 g/mol.
So in 2.92 grams there are 2.92/18.01528 = 0.1621 mol of particles.
1 mol contains 6,02214 × 10^23 particles by definition.
So the nr of H2O molecules is 0.1621 * 6,02214 × 10^23 = 0,9761 × 10^23.
Every molecule has 2 H atoms, so you have to double that.
2* 0,9761 × 10^23 = 1.952 × 10^23.
