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Atom: A) the basic unit of an element.
Atom is the smallest and structural unit of any element.
Particle: D) a tiny fragment or piece of matter.
A particle can be defined as a minute or small piece, fragment or portion of any matter. It may be used to access many physical and chemical properties such as density, volume, mass etc.
Phase: C) unique form of matter in which it can exist.
Phase can be defined as a particular state in which any matter can exists. Generally, matter can exists in three phases namely; solid, liquid, and gas. Plasma is the fourth phase which exists at very high temperature and pressure.
Scientific theory: B) an explanation for some naturally occurring event.
Scientific theory can be explained as a group of postulations or hypothesis formulated in order to explain naturally occurring phenomenon or event. These hypothesis are repeatedly confirmed with the help of experiments or observations.
