Question

What is described as a nucleus of protons and neutrons surrounded by an electron cloud?

Answer 1

That is the description of an atom, the basic unit of matter.

Explanation:

The diagram below cuts an atom in half so we can see how it is arranged. The protons (green) and neutrons (yellow) can be seen in the nucleus. The two shells that contain the electrons make up the electron cloud.

The ratio of the size of the nucleus to the electron cloud is `1:100,000`. An analogy that is often used is that if a pea were placed in the middle of a 100 yard football field, the pea would be the nucleus and the field would be the electron cloud. It's not a perfect analogy, but it does help to picture the size relationships between the nucleus and electron cloud of an atom.