How many molecules are present in 5 g of CaCO₃?

Correct answer: b 3.012 × 10²²

5/100 = 0.05 mole; 0.05 × 6.023 × 10²³ = 3.012 × 10²² molecules.

Why the other options are wrong

• a 3.012 × 10²³: 3.012 × 10²³ is half a mole, the count in 50 g; 5 g = 0.05 mole = 3.012 × 10²².
• c 3.012 × 10²¹: 3.012 × 10²¹ is the count in 0.5 g; 5 g holds 3.012 × 10²².
• d 3.012 × 10²⁰: 3.012 × 10²⁰ is the count in 0.05 g; 5 g holds 3.012 × 10²².