Term Definition
Atom A
Particle C
Phase B
Scientific Theory D
An atom is actually the smallest entity that is an identifiable element on the periodic table.
Phase is a solid liquid or gas.
A particle could be thought of as the size of a grain of sand. Still there are millions of atoms in such a particle.
These definitions are not the best in the world, but they are an improvement over what you were given. Study the answers carefully. You will have to know them.