Lithium has 2 stable isotopes Li-6 and Li-7. One of them has an abundance of 92.5% and the other has an abundance of 7.5%. Knowing the atomic mass of lithium is 6.941, which is the more abundant isotope?

Answer :  The more abundant isotope is, Li isotope-7

Explanation :

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

For Li isotope-7 :

Mass of Li isotope-7 = 7 amu

Fractional abundance of Li isotope-7 = 92.5 %

For Li isotope-6 :

Mass of Li isotope-6 = 6 amu

Fractional abundance of Li isotope-6 = 7.5 %

Average atomic mass of Li = 6.941 amu

As we know that the more abundant isotope is that whose percentage abundant will be more and atomic mass of isotope will be near to average atomic mass of isotope.

From this we conclude that, the percentage abundant of Li isotope-7 is more and their atomic mass is near to average atomic mass.

Hence, the more abundant isotope is, Li isotope-7

i do not get it   at all