Question

1 centimetre cube of a No 2 at STP contains how many atoms

Answer 1

1 mole of a gas at STP occupies 22400 cm³.
So  22400 cm³ contains 6.022*10²³ atoms or molecules.
So 1  cm³ contains 6.022*10²³/22400 =  2.688*10¹⁹ atoms or molecules.