Question

which of the following is unique for any given element?
a. the mass of the neutrons
b. the charge of the electrons
c. the number of protons
d. the number of neutrons

Explanation:

The number of protons in an atom defines the element. Each element has a unique atomic number which is equal to the number of protons. Neutron - number can vary (isotopes), electron - charge is always the same for electrons in general, and neutron - mass is standard for neutrons in general but not unique to an element.

Answer:

C. The number of protons