A sample of silicon has three naturally occurring isotopes: Si-28 (mass 28.0 amu); Si-29 (mass 29.0 amu) and Si-30 (mass = 30.0 amu). If the average atomic mass of silicon is 28.1 amu, which isotope is the most abundant?
A)Si-28
B)Si-29
C)Si-30
D)All isotopes have the same natural abundance.

Question

Quizplus · Accepted Answer

The most abundant isotope is the one with the closest mass to the average atomic mass, which is Si-28 (28.0 amu). If Si-29 or Si-30 were more abundant, the average atomic mass would be closer to their masses. Therefore, Si-28 must be the most common isotope.

A Sample of Silicon Has Three Naturally Occurring Isotopes: Si-28