Answer:
<span>2.49⋅<span>10<span>−12</span></span>moles Pb</span>
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 <span>6.022⋅<span>1023</span></span> 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 <span>1.50⋅<span>1012</span></span>atoms of lead.
Well, if you know that one mole of lead must contain <span>6.022⋅<span>1023</span></span> atoms of lead, it follows that you get <span>1.50⋅<span>1012</span></span> atoms of lead in
<span><span>1.50⋅<span>1012</span>atoms of Pb⋅<span>1 mole Pb<span>6.022⋅<span>1023</span>atoms of Pb</span></span></span><span>=<span>2.49⋅<span>10<span>−12</span></span>moles Pb</span></span></span>
