Question

which type of force holds protons and neutrons together in an atom?
electromagnetic force
gravitational force
strong nuclear force
contact force

Explanation:

The strong nuclear force is responsible for binding protons and neutrons together in the nucleus of an atom. Electromagnetic force acts between charged particles and is not the force holding nucleons together. Gravitational force is extremely weak at the atomic - scale and not relevant here. Contact force is a macroscopic concept and not applicable at the sub - atomic level for this purpose.

Answer:

strong nuclear force