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
