Which subatomic particle determines the elemental identity of an atom?

• A. Electron
• B. Proton
• C. Neutron
• D. Positron

Answer: (B)

Verified step by step guidance

1. Recall that the elemental identity of an atom is defined by the number of protons it contains in its nucleus. This number is called the atomic number (Z).
2. Understand that electrons are negatively charged particles orbiting the nucleus, and while they influence chemical behavior, they do not change the element itself.
3. Recognize that neutrons are neutral particles in the nucleus that contribute to the atom's mass and can create isotopes, but they do not affect the elemental identity.
4. Note that positrons are the antimatter counterparts of electrons and are not part of the normal atomic structure.
5. Therefore, the subatomic particle that determines the elemental identity of an atom is the proton, because changing the number of protons changes the element.