Q. The relative abundance of two isotopes of atomic weight 85 and 87 is 75% and 25% respectively. The average atomic weight of element is
A) 75.5
B) 85.5
C) 40.0
D) 86.0
Explanation
(b)
Average atomic weight
$= \frac{at.wt. \times relative\ abundance + at.wt.\ \times relative\ abundance}{100}$
$= \frac{85 \times 75 + 87 \times 25}{100}$
$= 85.5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.