in what reference are you asking?

please told what is one mole of H2?

Mole (unit) ... Thus, for example, one mole of water contains 6.02214076×10²³ molecules, whose total mass is about 18.015 grams – and the mean mass of one molecule of water is about 18.015 daltons. The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions.