Answer
The most abundant isotope is silicon-28, then the second most is silicon-29 and then the least abundant is silicon-30.
Work Step by Step
The correct atomic mass of silicon is 28.09 amu. The isotope silicon-28 has a atomic mass of 28 amu which is very close to the correct atomic mass of silicon thus it is more abundant in the atmosphere. The isotope silicon-30 has a atomic mass of 30 amu which is not very close to the correct atomic mass of silicon thus it is the least abundant in the atmosphere. The isotope silicon-29 has a atomic mass of 29 amu which is close to the correct atomic mass of silicon thus it is the the second most abundant in the atmosphere.
