Question

The nuclei of which one of the following pairs of nuclei are isotones?

• A. ₃₄Se⁷⁴, ₃₁Ga⁷¹
• B. ₄₂Mo⁹² , ₄₀Zr⁹²
• C. ₃₈Sr⁸⁴ , ₃₈Sr⁸⁶
• D. ₂₀Ca⁴⁰ ,₁₆S³²

Answer 1

The Correct Option is A

To determine which pair of nuclei are isotones, we need to understand what isotones are. Isotones are nuclei that have the same number of neutrons, but different numbers of protons.

Let's analyze each option to find the number of neutrons:

1. First Option: ₃₄Se⁷⁴, ₃₁Ga⁷¹

   Number of neutrons in Se: 74 - 34 = 40

   Number of neutrons in Ga: 71 - 31 = 40

   Both have 40 neutrons. Therefore, they are isotones.

2. Second Option: ₄₂Mo⁹², ₄₀Zr⁹²

   Number of neutrons in Mo: 92 - 42 = 50

   Number of neutrons in Zr: 92 - 40 = 52

   The number of neutrons is different, so they are not isotones.

3. Third Option: ₃₈Sr⁸⁴, ₃₈Sr⁸⁶

   Number of neutrons in the first Sr: 84 - 38 = 46

   Number of neutrons in the second Sr: 86 - 38 = 48

   The number of neutrons is different, so they are not isotones.

4. Fourth Option: ₂₀Ca⁴⁰, ₁₆S³²

   Number of neutrons in Ca: 40 - 20 = 20

   Number of neutrons in S: 32 - 16 = 16

   The number of neutrons is different, so they are not isotones.

Hence, the correct answer is the first option: ₃₄Se⁷⁴ and ₃₁Ga⁷¹ are isotones.