How many mol of PCl5 are in 0.17 g of PCl5?

2.56 × 10–3 mol of PCl5
3.81 × 100 mol of PCl5
3.54 × 101 mol of PCl5
8.16 × 10–4 mol of PCl5

the second one?

4 answers

moles = grams/molar mass
No, not #2. You're guessing.
You're still guessing. What is the molar mass of PCl5?
mols = grams/molar mass PCl5 = 0.17/molar mass PCl5 = ?
Use your calculator. Stop guessing. I suppose you realize that you have guessed twice and you have only two choices left. The next guess will tell you the correct answer. Let me see your work along with you answer.
3.54 x 10¹ mol of PCl5