Question

The relative abundance of two rubidiuin isotopes of atomic weights 85 and 87 are 75℅ and 25% respectively
average atomic wt of rubidiun is: -
(1) 75.5
12) 85.5
(3) 86.5
(4)87.5​

Answer 1

Answer:

85.5

Explanation:

Given that,

• relative abundance of rubidium isotope with atomic mass 85 = 75%
• relative abundance of rubidium isotope with atomic mass 87 = 25%

We know that,

Average atomic mass =

$\frac{ \Sigma \: relative \: abundance \times isotopic \: mass} {100}$

So,

$at. \: mass = \frac{85 \times 75 + 87 \times 25}{100} \\ \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 85.5$

Thus, the average atomic mass of Rubidium is 85.5.