Question

6.7 moles of carbon dioxide molecules contain how many molecules?

Answer 1

One mole is the amount having the same number of particles found in 12.000 grams of ¹²C (which is roughly 6.02x10²³). Thus, 6.7 moles of carbon dioxide contain $6.7 \cdot 6.02 \cdot 10^{23} = 4.03 \cdot 10^{24}$ molecules.