Question

The electronic configuration of an ion $M^{2+}$ is 2, 8, 14. If its mass 56, the number of neutrons in its nucleus is :

• A. 30
• B. 32
• C. 34
• D. 42

Answer 1

The correct option is A 30

$M^{2+}=2,8,14;\Rightarrow$ Electronic Configuration of $M=2,8,16$
So. total electrons in M will be $=26$
i.e., atomic number $\left(Z\right)=26$, Mass number (given) $=56$
$\therefore$ Number of neutrons$=A-Z=56-26=30$

Hence, the correct option is A.