What is a rule for determining the mass number of an atom?

1 Answer
Nov 8, 2015

Answer:

Mass number is the sum of the protons and neutrons in the atomic nucleus.

Explanation:

The mass number (#"A"#) is the sum of the atomic number (#"Z"#), which is the number of protons, and the number of neutrons (#"N"#) in the atomic nucleus of an isotope of an element. #"A=Z+N"#

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nucnot.html