<u>Answer:</u> The abundance of Si-28 isotope is the highest as compared to the other isotopes.
<u>Explanation:</u>
Average atomic mass is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.
Formula used to calculate average atomic mass follows:
We are given:
Three isotopes of Silicon, which are Si-28, Si-29 and Si-30.
Average atomic mass of silicon = 28.086 amu
As, the average atomic mass of silicon is closer to the mass of Si-28 isotope. This means that the relative abundance of this isotope is the highest as compared to the other two isotopes.
Percentage abundance of Si-28 isotope = 92.2%
Percentage abundance of Si-29 isotope = 4.7 %
Percentage abundance of Si-30 isotope = 3.1%
Hence, the abundance of Si-28 isotope is the highest as compared to the other isotopes.