Question

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

• A. ${}_{34}{\text{Se}}^{74}{,}_{31}{\text{Ga}}^{71}$
• B. ${}_{38}{\text{Sr}}^{84}{,}_{38}{\text{Sr}}^{86}$
• C. ${}_{42}{\text{Mo}}^{92}{,}_{40}{\text{Zr}}^{92}$
• D. ${}_{20}{\text{Ca}}^{40}{,}_{16}{\text{S}}^{32}$

Answer 1

Answer: (A)

${}_{34}{\text{Se}}^{74}{,}_{31}{\text{Ga}}^{71}$

The isotones have same number of neutrons. In given options ${}_{34}{Se}^{74}$ has $74-34=40{,}_{31}{Ga}^{71}$ has $71-31=40{,}_{38}{Sr}^{84}$ has $84-38=46{,}_{38}{Sr}^{86}$ has $86-38=48{,}_{42}{Mo}^{92}$ has $92-42=50{,}_{40}{Zr}^{92}$ has $92-40=52{,}_{20}{Ca}^{40}$ has $40-20=20,$ and ${}_{34}{Se}^{74}$ has $32-16=16$ neutrons. Hence isotonic pair is of ${}_{34}{Se}^{74}{,}_{31}{Ga}^{71}$

That is option A.