The atoms of different elements having the same number of neutrons but different number of protons are called as which of the following?

Option 1 -> Isobars have the same mass number but different atomic numbers (different protons AND different neutrons).

Option 2 -> Isotones have the same number of neutrons but different number of protons (different elements).

Option 3 -> Isotopes are atoms of the same element with same protons but different neutrons.

Option 4 -> Isoelectronic species have the same number of electrons, not related to neutrons.

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Hence, Option 2: Isotones -> Isotones are defined as atoms of different elements that contain the same number of neutrons in their nuclei while having different numbers of protons. For example, ¹⁴C (6 protons, 8 neutrons) and ¹⁵N (7 protons, 8 neutrons) are isotones -> correct