Question

What weight of oxygen gas will contain the same number of molecules as 56 gram of nitrogen gas?

Answer 1

For both of these gases to have the same number of molecules they would have to consist of equal moles. Number of moles of a substance is obtained by dividing the mass of substance needed by the molecular mass of the substance. Molecular mass of Nitrogen Gas N2 = 28 g.
Number of moles of Nitrogen in 56 g = 56/28 = 2 ...