which part of an atom is mostly empty space? \na. nucleus \nb. proton cloud \nc. electron cloud \nd. neutron

Brief Explanations:

An atom consists of a nucleus containing protons and neutrons at the center, surrounded by an electron - cloud. The nucleus is very small compared to the overall size of the atom, and the electron - cloud, which is the region where electrons move, is mostly empty space.

Answer:

C. electron cloud