Question

what is the average atomic mass of an element with isotopes a, b, and c?
a. $\frac{(mass of a)\times(% of a)+(mass of b)\times(% of b)+(mass of c)\times(% of c)}{3}$
b. $\frac{(mass of a + mass of b+mass of c)}{3}$
c. $(mass of a)\times(% of a)+(mass of b)\times(% of b)+(mass of c)\times(% of c)$
d. $\frac{(mass of a)}{(% of a)}+\frac{(mass of b)}{(% of b)}+\frac{(mass of c)}{(% of c)}$

Explanation:

Step1: Recall average atomic mass formula

The average atomic mass of an element with isotopes is calculated as the sum of the product of the mass of each isotope and its relative abundance (percentage). There is no division by 3 as the abundances are not equal - weighted in a simple - average sense.

Step2: Analyze each option

Option A divides the sum of products by 3 which is incorrect. Option B is a simple arithmetic mean of masses without considering abundances. Option D has an incorrect formula structure. Option C correctly represents the formula for average atomic mass as (mass of A)×(% of A)+(mass of B)×(% of B)+(mass of C)×(% of C).

Answer:

C. (mass of A) × (% of A) + (mass of B) × (% of B) + (mass of C) × (% of C)