Question

How does the number of molecules in 1 mol of oxygen compare with the number of molecules in 1 mol of nitrogen?
1 mol of oxygen has fewer molecules.
1 mol of oxygen has more molecules.
Each sample has the same number of molecules.
The molecules cannot be compared without knowing the mass.

Answer 1

Each sample has the same number of molecules.

One mole of any substance contains Avogadro's number of entities (~6.022×10^23). The masses differ (O2 ≈ 32 g/mol, N2 ≈ 28 g/mol), but the molecule count for 1 mol is the same.