The average atomic mass of a sample of an element X is16.2 u. Then the percentage of isotopes 16X8 and 18X8  is [[1]]% and [[2]]% respectively.

The average atomic mass of a sample of an element X is16.2 u. Then the percentage of isotopes

16

X

8

and

18

X

8

is 90% and 10% respectively.

Given,

The average atomic mass of X is 16.2 u.

Let the percentage of isotope

16

X

8

is A% and of

18

X

8

is (100-A)%.

So,

$\Rightarrow 16\times \frac{A}{100}+18\times \frac{100-A}{100}=16.2$

$\Rightarrow \frac{16A}{100}+\frac{1800-18A}{100}=16.2$

$\Rightarrow 1800-2A=1620$

$\Rightarrow 2A=180$

$\Rightarrow A=90$

So,

16

X

8

is 90% and

18

X

8

is 10% (100-A)= (100-90)=10%.