Question

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

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

Answer 1

Answer: (A)

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

Answer 2

The nuclei which have same number of neutrons but different atomic number and mass number are known as isotones. In choice $(a)$ nuclei of ${ }_{34} Se ^{74}$ and ${ }_{31} Ga ^{71}$ are isotones as
$A-Z=74-34=71-31=40$