Question
Question: The relative abundance of two isotopes of atomic weight 85 and 87 is 75% and 25% respectively. The a...
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
87.5
D
86.0
Answer
85.5
Explanation
Solution
Average atomic weight/ The average isotopic weight
& \text{\% of 1st isotope } \times \text{ relative mass of 1st isotope } + \\ & \text{\% of 2nd isotope } \times \text{ relative mass of 2nd isotope} \end{aligned}}{\text{100}}$$ $$= \frac{85 \times 75 + 87 \times 25}{100} = 85.5$$