Question

2 which subatomic particle defines an element? a mass number b electron c neutron d proton

Explanation:

The number of protons in the nucleus of an atom, known as the atomic number, determines the identity of an element. Different elements have different numbers of protons. Electrons are involved in chemical bonding, neutrons affect the mass and isotopic form, and mass - number is the sum of protons and neutrons.

Answer:

D. proton