Question

can a particle be single atom

Answer 1

No

Answer 2

A atom is the smallest living thing. So basically that means no it is not

Answer 3

no :)

Answer 4

"atom is the smallest living thing" - nope, that would be a cell.

I'm pretty sure a single atom \(can\) be regarded as a particle. Look at it's definition:

"In the physical sciences, a particle is a small localized object to which can be ascribed several physical or chemical properties such as volume or mass." http://en.wikipedia.org/wiki/Particle

"Particle" only implies a unit, and further derivatization is needed to narrow it's meaning. Like, subatomic-, elementary-, atomic particles.

"Atoms are the smallest neutral particles into which matter can be divided by chemical reactions. An atom consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons." http://en.wikipedia.org/wiki/List_of_particles