У 2грамах воднню скільки молекул і скільки атомів

In 2 g H₂ there are 6,023.10²³ molecules H₂ and 2 x 6,023.10²³ atoms H

The mole is the number of particles contained in a substance

1 mol = 6.02.10²³

Moles can also be determined from the amount of substance mass and its molar mass

The question is :

in 2 grams of hydrogen how many molecules and how many atoms

MW H₂ = 2.01568 u  (2 atoms of H)

MW H = 1.00784 u

Or a simply way :

1 g of H atoms = 1 mol of H  (MW H = 1 g/mol)

2 g of H atoms (in 2 gr H₂) = 2 moles of H  

2 g of H₂ molecules = 1 mole of H₂  (MW H₂=2 g/mol)

so in 2 g H₂ there are 6,023.10²³ molecules H₂ and 2 x 6,023.10²³ atoms H

there is none because earth is stationary and flat.