Which of the following have the same number of atoms?
a. 2 grams of lead and 2 grams of carbon,
b. 2 moles of lead and 2 moles of carbon,
c. 2 moles of lead and 2 grams of lead,
d. 1 gram of carbon and 2 grams of carbon
Science is not my specialty, but I think I have an answer for you. Based on what I understand about chemistry, the correct answer to your problem would be: B.
Let's look at why.
A) This answer cannot be correct. Though 2 grams of lead and 2 grams of carbon would weigh the same, they would not contain the same number of atoms because they have different atomic weights. Only 2 grams of the same elements would have the same number of atoms.
C) This answer is not correct because of the definition of "mole." A mole is a specific number of atoms, roughly 600,000 billiion billions. A gram is a measure of weight, not atoms.
D) Same type of wrongness. Both are using carbon, but one is double the weight. It couldn't have the same number of atoms and still be twice as may grams.
That leaves us with B. Because a mole is a measure of the number of atoms, it doesn't matter that one is carbon and the other is lead. If you have one of each, you have the same number of atoms because a mole isn't a measurement of weight. One mole of "this" is the same as one mole of "that."
Hope this makes sense!
The answer is b. Since they have two moles, which means they have two times the Avogardro's constant, their atoms must be the same.
Chemistry is my specialty and ophelious is right - explanation and all - couldn't have put it better myself (hope this makes you more confident about choosing b :-)