2. Which of the following pair represents isotones?
(1) ³H, ⁴He                                           (2) ¹⁵N, ¹⁴N1
(3) ¹⁴⁰Ba, ¹⁴⁰Th                                     (4) ¹H, ³H

Understanding Isotones: A Guide to Identifying Nuclear Similarities

What Are Isotones?

Isotones are atoms of different elements that have the same number of neutrons but different numbers of protons. They play a crucial role in nuclear science and various research applications.

How to Identify Isotones?

H1: The Composition of Isotones

To determine isotones, we look at the neutron number:

• Neutron number = Mass number – Proton number

H2: Given Options Analysis

Let’s analyze the given pairs:

1. 3H (Tritium) and 4He (Helium-4):
   • Tritium (3H): 1 proton, 2 neutrons
   • Helium-4 (4He): 2 protons, 2 neutrons
   • Different neutron numbers → Not isotones.
2. 15N (Nitrogen-15) and 14N (Nitrogen-14):
   • 15N: 7 protons, 8 neutrons
   • 14N: 7 protons, 7 neutrons
   • Different neutron numbers → Not isotones.
3. 140Ba (Barium-140) and 140Th (Thorium-140):
   • 140Ba: 56 protons, 84 neutrons
   • 140Th: 58 protons, 84 neutrons
   • Same neutron number → Isotones! ✅
4. 1H (Protium) and 3H (Tritium):
   • 1H: 1 proton, 0 neutrons
   • 3H: 1 proton, 2 neutrons
   • Different neutron numbers → Not isotones.

Correct Answer

The correct pair of isotones is:

(3) 140Ba and 140Th

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