If an atom of tin has a mass number of 118 and an atomic number of 50, how many neutrons are in its nucleus?

1 Answer
Oct 28, 2016


There must be 68 neutrons in a #""^118Sn# isotope.


The mass number relates to the massive particles: protons, and neutrons. Since there are 50 protons, there MUST be 68 neutrons.

Note that an examiner would be quite justified in asking you this question WITHOUT advice as to #Z#, the atomic number, if tin metal were specified. Do you agree?