Question

Why is the average atomic mass used when calculating grams of a

substance?
A. The average atomic mass is known to more significant figures.
B. The elements in the substance are mixtures of their isotopes.
C. The exact weights of the isotopes are not known.
D. The number of isotopes in the sample is constantly changing.

Answer 1

I guess the answer is B

Answer 2

B. The elements in the substance are mixtures of their isotopes.