A mole of oxygen O2 and a mole of phosphorus P4 do not contain the same number of molecules.

Yes, that statement is correct. A mole is defined as the amount of substance that contains as many entities (usually atoms or molecules) as there are in 12 grams of carbon-12. It is important to note that a mole of any substance contains Avogadro's number of entities, which is approximately $6.022 \times 10^{23}$.

1. Mole Calculation

   • A mole of $O_2$ (oxygen gas) contains $6.022 \times 10^{23}$ molecules of $O_2$.
   • A mole of $P_4$ (tetraphosphorus) is a different case. Since each molecule of $P_4$ contains 4 phosphorus atoms, the count is still in terms of molecules.

2. Comparison of Entities

   • Since one mole of $P_4$ corresponds to one molecule of $P_4$, the quantity here is:
     • Molecules of $O_2$: $6.022 \times 10^{23}$ molecules
     • Molecules of $P_4$: 1 molecule

3. Conclusion

   • Therefore, a mole of $O_2$ contains $6.022 \times 10^{23}$ molecules, while a mole of $P_4$ contains only 1 molecule.

In summary, although both contain a mole of substance, a mole of oxygen gas ($O_2$) has millions of molecules compared to just one molecule in a mole of phosphorus ($P_4$). This highlights how the molecular composition differs significantly between the two substances.