Isotopes share protons but differ in neutrons

Steps:

• Isotopes are variants of the same element, defined by identical atomic numbers.
• Atomic number equals the number of protons, which determines the element.
• Neutral atoms have equal protons and electrons, so isotopes share electron count.
• Mass number varies due to different neutron counts in isotopes.

Why B is correct:

• By definition, isotopes of the same element have the same atomic number (protons) but different mass numbers from varying neutrons.

Why the others are wrong:

• A: Neutral isotopes have the same electrons, matching proton count.
• C: Isotopes differ in neutrons, not electrons.
• D: Same neutrons would mean identical isotopes, not variants.

Final answer: B