Proton properties.

• A. Found in nucleus; negative charge; determines element's identity.
• B. Found in electron shells; negative charge; determines atomic number.
• C. Found in nucleus; neutral charge; mass determines element.
• D. Found in nucleus; positive charge; number of protons determines element's identity and atomic number.

Answer: (D)

Protons sit in the nucleus and carry a positive charge. The number of protons is what defines the atomic number, which uniquely identifies the element on the periodic table. So the element’s identity and its atomic number are set by how many protons there are. The nucleus also contains neutrons, and together protons and neutrons give the atom its mass, but varying neutrons changes the mass without changing the element. Electrons orbit in shells and have negative charge; they influence chemical behavior but do not determine which element it is. That’s why describing protons as nucleus-based, positively charged particles whose count determines the element’s identity and atomic number is the correct understanding.