13. The subatomic particle that contributes mass and a single positive charge to an atom is the a. proton b. neutron c. electron

a. proton

Explanation:

Proton -

It is on of the subatomic particle of the atom, it is positively charged, with the symbol of p⁺, i. e., a single positive charge.

The mass of proton and the neutrons together contributes to the mass of the atom.

All the elements have their specific number of proton and mass number, denoted by Z.

Hence, from the given options the correct answer is a. proton.