Indium has atomic number 49 and atomic mass 114.8 g. contains a mixture of indium-112 and indium-115

Indium has atomic number 49 and atomic mass 114.8 g. contains a mixture of indium-112 and indium-115 in an atomic ratio of approximately

A) 6/94.

B) 25/75.

C) 50/50.

D) 75/25.

E) 94/6.

The atomic mass given in the problem (or found on the Periodic Table) is the average of the atomic masses of isotopes taking into account their % abundance. The more abundant an isotope is, the more it will contribute to the atomic mass. In the problem there are two isotopes: indium-112 and indium-115 with their atomic masses of 112 and 115 respectively. Since the atomic mass presented in the problem is 114.8g, it is very close to the mass of the second isotope indium-115, indicating that this isotope must have a very high % abundance such as in choice A: 6/94. We can check the choice by calculating the average atomic mass with a 6% abundance indium-112 and 94% abundance indium-115.