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Some atomic species of the same element differing in mass are called ________.

Asked in GUJCET 2024 · Composition, isotopes and isobars

• (1) Isotone
• (2) Isobar
• (3) Isomar
• (4) Isotope

Step-by-step solution

Why the other options are wrong

• (1) Isotones share the neutron number N and differ in Z, so they are different elements — ¹⁹⁸₈₀Hg and ¹⁹⁷₇₉Au, both with 118 neutrons.
• (2) Isobars share the mass number A and differ in Z — ³₁H and ³₂He. They are different elements and have the same mass, the opposite of what is described.
• (3) Printed as 'Isomar', which is not a term in nuclear physics. The word it resembles, isomer, means one and the same nuclide (same Z, same A) held in a long-lived excited state — again not a difference of mass.

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