Question 8
How many molecules are there in 10 g of oxygen (O2)? (Mr = 32, L = 6.022 × 1023)
The right answer is the one marked above.
1.88 × 1023. First the moles: 10 ÷ 32 = 0.3125 mol. Then 6.022 × 1023 × 0.3125 = 1.88 × 1023.
1.93 × 1024 comes from inverting the division and taking 32 ÷ 10. Going from a mass to a number of particles must always pass through moles.