Question

An element of atomic weight Z consists of two isotopes of mass number Z-1& Z+2.percentage of abundance of heavier isotopes

Answer 1

Let the percentage of heavier isotope = x
Percentage of lighter isotope = 100-x

Z = [(Z+2)x +  (Z-1)(100-x)]/100
100Z = Zx + 2x + 100Z - Zx - 100 +x
3x - 100 = 0 or x = 33.33

The percentage of heavier isotope = 33.33%

Answer 2

Answer: 66.66 %

Explanation:

Given,

Mass of isotope 1 = Z-1

% abundance of isotope 1 = x% =$\frac{x}{100}$

Mass of isotope 2 = Z+2

% abundance of isotope 2 = (100-x)%=$\frac{100-x}{100}$

Formula used for average atomic mass of an element :

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

$Z=\sum[(Z-1\times \frac{x}{100})+(Z+2\times \frac{100-x}{100})$

Solving for x, we get

$x=66.66%$