Question

find the error with subject - verb agreement. select the incorrect verb and type it correctly. the number of protons in an atom are expressed by that elements atomic number on the periodic table.

Explanation:

The subject "The number of protons" is singular. In subject - verb agreement, a singular subject requires a singular verb. "Are" is a plural verb, so it should be changed to "is".

Answer:

The incorrect verb is "are", and it should be "is".