Question

galliums atomic mass is 69.72 amu, what isotope of gallium is most likely the most abundant?
gallium - 71
gallium - 68
gallium - 69
gallium - 70

Explanation:

Step1: Recall atomic - mass concept

The atomic mass of an element is a weighted - average of the masses of its isotopes, with the most abundant isotope having the greatest influence on the atomic mass value.

Step2: Calculate mass differences

Calculate the differences between the given atomic mass (69.72 amu) and the masses of each isotope.

• For Gallium - 71: $|71 - 69.72|=1.28$
• For Gallium - 68: $|68 - 69.72| = 1.72$
• For Gallium - 69: $|69 - 69.72|=0.72$
• For Gallium - 70: $|70 - 69.72| = 0.28$

Step3: Determine the closest isotope

The isotope with the mass closest to the atomic mass of gallium (69.72 amu) is the most likely to be the most abundant. Gallium - 69 has the smallest mass difference.

Answer:

Gallium - 69