Question

079.
Average atomic weight of an element M is
51.7. If two isotopes of M, M50 and M52
are present, then percentage of occurrence
of M30 in nature will be.
(A) 85%
(B) 15%
(C) 50% (D) 100%
​

Answer 1

Answer:

The correct answer is option (B).

Explanation:

Solution : Given,

Mass of isotope 1 =50 u

fractional  abundance of isotope ,M-50 = x

Mass of isotope 2 = 52 u

fractional abundance of isotope ,M-52 = (1-x)

Formula used for average atomic mass of an element :

$\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})$

$51.7 u=50 u\times x+52 u\times (1-x)$

$x = 0.15=\frac{015}{100}=15\%$

The correct answer is option (B).