Answer: 1 mol of oxygen, O₂, and 1 mol of CO will have the same number of molecules, and the same number of atoms.
Justification:
Althought the question is too open, other answers may arise, the most remarkable similarity between the two compounds is that both are diatomic.
That means that both molecules oxygen, O₂, and carbon monoxide, CO have two atoms.
So, 1 mol of oxygen, O₂, and 1 mol of CO will have the same number of molecules, and the same number of atoms.
You must remember that 1 mol means a specific number. It is Avogadro's number, which is 6.022 × 10 ²³.
So 1 mol of CO and 1 mol of O₂ are the same number of representative particles: 6.022 ×10²³ molecules eac, and two times that number of atoms each (since each molecule has two atoms).