Chlorine has two isotopes with masses 34.98 u and 36.98 u occurring in abundances of 75.4% and 24.6% respectively. What will the average mass of chlorine be?

35

The correct answer is option 4: 35

Average atomic mass = (mass₁ × abundance₁) + (mass₂ × abundance₂)

= (34.98 × 75.4%) + (36.98 × 24.6%)
= (34.98 × 0.754) + (36.98 × 0.246)
= 26.37 + 9.09
= 35.46 u