The number of neutrons in the dipositive zinc ion (Mass no. of Zn 65 = )

Atomic number of Zinc (Zn) is 30. It means there are 30 protons present in Zn. Mass no. of Zn is 65. In dipositive zinc ion, there are two electrons less than that of no. of electrons in neutral Zn. But there is no change in no. of protons or neutrons in ${\mathrm{Zn}}^{+2}$ ion.

Hence, no. of neutrons in ${\mathrm{Zn}}^{+2}$ion is n =A- Z 

 n= 65- 30= 35