Question

The electronic configuration of a dipositive ion $M^{2+}$ is $2,8,14$ and its mass number is $56$. The number of neutrons present is

• A. 32
• B. 42
• C. 30
• D. 34

Answer 1

Answer: (C)

Number of electrons in $M^{2+}=24$
$\therefore$ number of electrons in $M=26$
i.e., atomic number $(Z)=26$
Mass number $(A)=56$
$\therefore$ number of neutrons
$=A-Z=56-26=30$ .