Question

the atomic mass of an element X is 16.24 . what are the percentages of isotopes an X having atomic number 8 and mass numbers 16 and 18

Answer 1

The isotope of X with mass 16 will have 88%.
The isotope of X with mass 18 will have 12%.

Answer 2

Let the % of isotope ₈¹⁶X = x

Let the % of isotope ₈¹⁸X = 100 - x

Average atomic mass of an element X = 16.24

Now,

Average atomic mass=[(Mass of ₈¹⁶X )(% of ₈¹⁶X)+(Mass of ₈¹⁸X)(% of ₈¹⁸X)]/100

16.24 = (x) (16)+(100-x) (18)] / 100

16.24 = (16x + 1800 - 18x) / 100

1624 = 1800 - 2x

2x = 1800 - 1624

2x = 176

x = 176/2

x = 88

Hence, % of isotope ₈¹⁶X = 88%

and % of isotope ₈¹⁸X = 100 - 88 = 12%

This is the required answer.

Thanks.