The number of in the atom is what determines whether the atom is a potassium atom, a hydrogen atom, or an oxygen atom.

proton
neutron
electron
quark

The correct answer is proton.

Explanation:

Atom is a smallest unit of the matter. It consists of proton, neutron and electrons. They are the subatomic particle of the atom.

Electron is negatively charged particle. Proton is a positively charged particle.

Neutron has no charge.

Atomic number of the atom is equal to the number of protons present in the nucleus of the atom. It identifies the chemical element.

In an atom having no charge, the atomic number is equal to the number of electrons.

If the atom is negatively or positively charged, then the number of electrons will vary.

Therefore, The number of proton in the atom is what determines whether the atom is a potassium atom, a hydrogen atom, or an oxygen atom.

b) phosphorus pentoxide