Chlorine has two isotopes of masses $34.98 ext{ u}$ and $36.98 ext{ u}$ with relative abundances o

Question

Chlorine has two isotopes of masses $34.98	ext{ u}$ and $36.98	ext{ u}$ with relative abundances of $75.4\%$ and $24.6\%$ respectively. The average mass of a chlorine atom is closest to:

Professor PC Thomas Classes · Answer

The average atomic mass is the weighted average of the isotopes: $(75.4 	imes 34.98 + 24.6 	imes 36.98) / 100 = 35.47	ext{ u}$.