What is the relative atomic mass of an element whose one atom has mass 3.16 × 10⁻²³ g?

Correct answer: b 19

Actual mass × Avogadro number = 3.16 × 10⁻²³ × 6.023 × 10²³ = 19 (F).

Why the other options are wrong

• a 9: 9 would need 1.49 × 10⁻²³ g; 3.16 × 10⁻²³ × 6.023 × 10²³ = 19.
• c 27: 27 is Al, whose atom weighs 4.48 × 10⁻²³ g; here it is 19.
• d 32: 32 (S) would need 5.31 × 10⁻²³ g; here it is 19.