How does the number of molecules in 1 mol of oxygen compare with the number of molecules in 1 mol of nitrogen ?

Each sample has the same number of molecules;
According to the Avogadro's number, or constant, one mole of a substance contains 6.022 × 10^23 constituents particles, usually atoms or molecules.
Therefore, 1 mole of oxygen contains 6.022 × 10^23 molecules,similar to  1 mole of nitrogen, which also contains 6.022 ×10^23 molecules

Is a logical series of steps