simplest form of matter?

Question

The simplest form of matter can be called

Answer 1

An atom, if you wanted the simplest form that has unique properties.

There are subatomic particles, but they are no longer unique substances

Answer 2

When we look at other galaxies we see that the whole galaxy is rotating at the same speed. If there was only the matter we see acting on the galaxy, the center would rotate faster than the arms. What we see implies that there is some sort of matter acting there that we can not see, thus the name "dark matter."

Answer 3

an atom.