Question

The number of neutrons in dipositive zinc ion with mass number 70 is:

• A. 34
• B. 36
• C. 38
• D. 40

Answer 1

The correct option is D 40

Mass number of Zinc = 70 which is also same in $Z{n}^{2+}$ since number of protons are not affected.
$\text{Atomic number}=\text{number of proton= 30}$
$\text{Number of neutron = mass number - number of proton =70 - 30 = 40}$
We know that in $Z{n}^{2+}$ number of proton and number of neutrons will be same as that of $Zn$. So, the number of neutrons is 40.