6.02 * 10^23 atoms of nitrogen in one mole of nitrogen gas but nitrogen gas is diatomic so multiply it by 26.02*10^23 * 2

1 mole of a substance contains Avogadro's number of molecules . This number is 6.02 *10^23, therefore one mole of oxygen gas contains 6.02*10^23 molecules

One mole of iron weighs 58.85 grams which is the answer

But can you further elaborate on the first 2 questions?

Oxygen and Nitrogen are both diatomic so the 1 Mole of each should be doubled. In other words you would need to multiply Avogadros number by 2 which would equal approximately 12.044*10^23.

Yes that is right one mole of any element has a mass in grams which is equal to its atomic number and has exactly 6.02*10^23 atoms. Oxygen and Nitrogen are both diatomic so we will multiply Avogadros number by 2