How does an electron relate to energy level?

Question

How does subatomic particles relate to atomic unit?

The reviews ask for 1 to 2 sentences.

Answer 1

I have struggled with this question and I don't know how to answer it.
Electrons are in energy levels. But that doesn't seem to answer the question to me.
If we call subatomic particles the neutron, proton, and electron, then neutrons and protons have approximately the same mass (1 amu) and electrons have a mass of about 1/1800 that amount (essentially 0 amu). Again, I don't know that this anwers the question.