Question

a sample of bromine contains the following relative abundances of its isotopes
isotope | relative abundance
$_{35}^{79}$br | 50.69%
$_{35}^{81}$br | 49.31%
what is the average relative atomic mass of the bromine in the sample?

Explanation:

Step1: Convert percentages to decimals

For \(^{79}_{35}\text{Br}\), \(50.69\% = 0.5069\); for \(^{81}_{35}\text{Br}\), \(49.31\% = 0.4931\).

Step2: Calculate weighted sum

Multiply each isotope's mass by its abundance and sum:
\(79\times0.5069 + 81\times0.4931\)
\(= 40.0451 + 39.9411\)
\(= 79.9862\)

Answer:

\(79.99\) (or \(79.9862\), rounded appropriately)