Q. 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
Explanation
(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
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.