CORRECT answer is Isobars. Isotope: It is defined as the atoms which have the same number of protons (or same atomic number) but having different neutrons. ISOBAR: The nuclei which have the same mass number (A) but a different atomic number (Z) are called isobars. Isotone: The nuclei having an EQUAL number of neutrons (A-Z) but different numbers of protons (Z) and different mass numbers (A) are called isotones.Allotrope: ALLOTROPY or allotropism is the property of some chemical elements to exist in two or more different forms in the same physical state KNOWN as allotropes of the elements. Allotropes are different structural modifications of an element.Explanation:In the isobars, the number of electrons, proton,s, and neutron are different because isobars are different elements having the same atomic mass. For Ex: 40S, 40Ar, 40K, and 40Ca.So, the number of electrons, protons, and neutrons are different in isobars.