Please help me with this question.
What particle has exactly one quantums unit of charge?
an electron has one unit of charge.
Your use of quantum is unusual, in the standard model of matter, their is a number of types of charge, and the particle that carries most is the guage boson. I doubt if your teacher meant this meaning in the use of quantum, however, it is the answer to what was asked.
http://en.wikipedia.org/wiki/Charge_(physics)
To find the particle that has exactly one quantum unit of charge, we need to understand some basics of quantum physics and elementary particles.
The fundamental unit of charge in quantum physics is the elementary charge denoted as "e." It is the charge of a proton or the negative charge on an electron.
Now, let's consider the particles that have charge 1e or -1e:
1. Proton: A proton has a charge of +1e (or simply written as +e). It is a subatomic particle that is found in the nucleus of an atom.
2. Electron: An electron has a charge of -1e (or simply written as -e). It is a subatomic particle that orbits around the nucleus of an atom.
These are the only two particles in nature known to have a charge that is a whole number multiple of the elementary charge (±e), where +e represents a positive charge and -e represents a negative charge.
Therefore, the particle that has exactly one quantum unit of charge is an electron, which has a charge of -1e.