Which subatomic particle, when its number in the nucleus changes, changes an atom’s elemental identity?

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

Answer: (A)

Verified step by step guidance

1. Recall that an atom's elemental identity is determined by its atomic number, which is the number of protons in the nucleus.
2. Understand that changing the number of protons changes the atomic number, thereby changing the element itself.
3. Note that electrons are involved in chemical reactions and charge but do not change the element when their number changes.
4. Recognize that neutrons affect the isotope of an element but do not change the elemental identity because the atomic number remains the same.
5. Photons are particles of light and are not subatomic particles within the atom, so they do not affect elemental identity.