Question

how many atoms of hydrogen and oxygen are present in 0.15 mole of water ?

Answer 1

There is one moles of oxygen atoms per mole of water (given by the formula H2O). There are Avogadro's number of particles in every mole of anything (6.02 x 10^23), so there are 0.16 x 6.02 x 10^23 individual oxygen atoms in 0.16 moles of water, or 9.64 x 10^22.