The number of hydrogen atoms in 2 g of hydrogen gas (H2) is (Avogadro number N = 6.022 x 10^23)

The molar mass of H2 is 2 g/mol, so 2 g is 1 mole of molecules, that is 6.022 x 10^23 molecules. Each molecule has two atoms, so the atoms number 2 x 6.022 x 10^23 = 1.2044 x 10^24. Writing 6.022 x 10^23 counts only molecules. The option 3.011 x 10^23 would be for a half mole, and the last is four times the molecule count.