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

Options

A. `""_38Sr^84 , ""_38Sr^86`
B. `""_34Se^74, ""_31Ga^71`
C. `""_20Ca^40, ""_16S^32`
D. `""_42Mo^92 , ""_40Zr^92`

Answer

B

Explanation

Isotones have the same number of neutrons.
In (b), `""_34Se^74 , A - Z = 74 - 34 = 40`
and in `""_31Ga^71 , A-Z = 71 - 31 = 40`
Thus `""_34Se^74 " and " ""_31Ga^71` are isotones as they have the same number of neutrons.
But in (d), 92 - 42 `ne` 91 - 40
In (a), 84 - 38 `ne` 86 - 38
In (c ) , 40 - 20 `ne` 31 - 16
Thus nuclei given in (a), (c), and (d) are not isotones.