Question

Relative abundance of isotopes of carbon are as follows:-

Isotopes	Relative abundance	Atomic Mass
C-12	$98.892$	12
C-13	$1.108$	13.00335
C-14	$2\times {10}^{-10}$	14.00317

The average atomic mass of carbon will be:-

• A. 16.0056 u
• B. 12.001 u
• C. 15.001 u
• D. 10.001 u

Answer 1

The correct option is B 12.001 u

The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance.

Atomic Weight =(% abundance isotope 1)×mass of isotope 1 +(% abundance isotope 2)×mass of isotope 2 +(% abundance isotope 3)×mass of isotope 3 /100
Hence, average atomoc weight of C =
$\frac{(98.892\times 12)+(1.108\times 13.00335)+(2\times {10}^{-10}\times 14.00317)}{100}$

= 12.001 u