Question

what fundamental force keeps protons from repelling each other and flying apart?
a electrostatic force
b weak nuclear force
c strong nuclear force
d gravity

Explanation:

Protons are positively charged. Electrostatic force (a) would cause them to repel. Gravity (d) is too weak at the nuclear scale. The weak nuclear force (b) is involved in processes like radioactive decay. The strong nuclear force (c) acts over short distances in the nucleus to bind protons (and neutrons) together, overcoming the electrostatic repulsion.

Answer:

C. strong nuclear force