Question

What is the simplest type of particle?

Answer 1

Particle is more than an atom - a particle I beleive implies either a diatomic gas or just a plain old unbonded noble gas atom? hope this helped.

Answer 2

Can't get any 'simpler' than the atom. An atom contains three particles, however; a neutron (neutral), proton (positive) and an electron (negative). I hope this is what you were looking for.