Nucleon number is the mass number of an isotope

Steps:

• Identify the isotope notation: U-235 means uranium with mass number 235.
• Recall that nucleon number is the total of protons and neutrons in the nucleus.
• Uranium's atomic number is 92, so protons = 92; neutrons = 235 - 92 = 143.
• Thus, total nucleons = mass number = 235.

Why C is correct:

• By definition, the nucleon number (A) is the mass number in isotopic notation like U-235, where A = 235.

Why the others are wrong:

• A: This is uranium's atomic number (protons only), not total nucleons.
• B: This is the number of neutrons (235 - 92), not total nucleons.
• D: This exceeds the mass number and has no basis in uranium isotopes.

Final answer: C