Question

The isotopes of an element have mass numbers A, A + 1, A + 2. The ratio of abundance of these isotopes is $3:2:4$. Calculate the average atomic mass of the element.:

• A. $A+\frac{10}{9}$
• B. $A+\frac{9}{10}$
• C. 9A + 10
• D. 10A + 9

Answer 1

Answer: (A)

$A+\frac{10}{9}$

The average atomic mass of the element
$=\frac{[3\times A]+[2\times (A+1\left)\right]+[4\times (A+2\left)\right]}{3+2+4}$
$=\frac{\left[3A\right]+[2A+2]+[4A+8]}{9}$
$=\frac{9A+10}{9}$
$=A+\frac{10}{9}$