Question

An element A exist in two isotopic forms A15 and
A16. If the average atomic mass of A was found to
be 15.24, then the % relative abundance of A15 will
be
(1) 10%
(2) 20%
(3) 40%
(4) 76%
​

Answer 1

Answer:

Percentage relative abundance of A^{15}A

15

isotope is 76%

Explanation:

We are given the average atomic mass of element A which is 15.24 amu.

Formula of average atomic mass:

\text{Average Atomic Mass}=\sum_{i=1}^{n}(\text{Fractional abundance})_i\times (\text{Mass number})_iAverage Atomic Mass=∑

i=1

n

(Fractional abundance)

i

×(Mass number)

i

We take fractional abundance of A^{15}A

15

isotope = x

Mass of A^{15}A

15

isotope = 15 amu

Fractional abundance of A^{16}A

16

isotope = (1 - x)

Mass of A^{16}A

16

isotope = 16 amu

Putting all the values in the above equation, we get

15.24=(15\times x)+(16\times (1-x))15.24=(15×x)+(16×(1−x))

x=0.76x=0.76

We are supposed to find the percentage abundance, so we multiply the fractional abundance by 100.

\%\text{ abundance}=0.76\times 100% abundance=0.76×100

Percentage abundance of A^{15}A

15

= 76%

option no 4