The correct answer is C: mass numbers are equal.. Isobars are atoms of different elements that have the same mass number (A) but different atomic numbers (Z). For example, ⁴⁰Ar (Z=18) and ⁴⁰Ca (Z=20) are isobars — both have mass number 40, but different atomic numbers, electron counts, and neutron counts.
A.atomic numbers are equal.
B.the number of electrons is equal.
C.mass numbers are equal.✓ Correct
D.the number of neutrons is equal.
Explanation
Isobars are atoms of different elements that have the same mass number (A) but different atomic numbers (Z). For example, ⁴⁰Ar (Z=18) and ⁴⁰Ca (Z=20) are isobars — both have mass number 40, but different atomic numbers, electron counts, and neutron counts. Atoms with equal atomic numbers (and hence equal electrons) are isotopes (same element), while atoms with equal numbers of neutrons are called isotones.
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