2.49⋅10−12moles Pb
Explanation:Before doing any calculations, it's worth noting that atoms do not contain moles, it's the other way around.
A mole is simply a collection of atoms. More specifically, you need to have exactly 6.022⋅1023 atoms of an element in order to have one mole of that element - this is known as Avogadro's number.
In your case, you must determine how many moles of lead would contain 1.50⋅1012atoms of lead.
Well, if you know that one mole of lead must contain 6.022⋅1023 atoms of lead, it follows that you get 1.50⋅1012 atoms of lead in
1.50⋅1012atoms of Pb⋅1 mole Pb6.022⋅1023atoms of Pb=2.49⋅10−12moles Pb
