Isotopes share the same atomic number but differ in neutron count

Steps:

• Uranium (U) has atomic number 92, so ²³⁰U has 92 protons and 230 - 92 = 138 neutrons.
• Isotopes of the same element have identical proton numbers but varying neutrons.
• Check options for 92 protons with a neutron count ≠ 138.
• Option C matches: 92 protons, 136 neutrons (different from 138).

Why C is correct:

• By definition, isotopes have the same atomic number (protons) but different mass numbers, so 92 protons and 136 neutrons (mass 228) is another uranium isotope.

Why the others are wrong:

• A: 90 protons means thorium, not uranium.
• B: 91 protons means protactinium, not uranium.
• D: 93 protons means neptunium, not uranium.

Final answer: C