Protons and neutrons are composed of these fundamental particles. The other fundemental particles are leptons, like electrons and neutrinos. A proton is composed of three quarks. An atom is composed of a nucleus that includes protons and neutrons, surrounded by a cloud of electrons. A molecule is two or more atoms sharing electrons.
Dust consists of very small pieces of solid matter distributed diffusely through space.
Their sizes are on the order of the width of a human hair. Meteoroids are small chunks of rock, from the size of sand grains up to hundreds of meters in length, that orbit about the Sun. An asteroid is a large chunk of rock that orbits the Sun. Asteroids are bigger than meteoroids and are found in sizes up to several hundred kilometers. Most asteroids orbit the Sun between the orbits of Mars and Jupiter.