Question

The relative abundance of two isotopes of atomic weight 85 and 87 is 75%and 25%respectively .The average atomic weight of the element is

Answer 1

Answer:

See below.

Explanation:

We have the atomic masses of two isotopes namely,

$A_1 = 85\\A_2 = 87$

Their relative abundance is,

$\delta A_1 = 0.75 \\\delta A_2 = 0.25$

The average atomic weight will be,

$\bar{A}  = A_1 \times \delta A_1 + A_2 \times \delta A_2 \\= 85 \times 0.75 + 87 \times 0.25 \\= 63.75 + 21.75\\= 85.5$