Q. The atomic numbers of elements $X$, $Y$ and $Z$ are 19, 21 and 25 respectively. The number of electrons present in the $M$-shell of these elements follow the order
A) $Z > X > Y$
B) $X > Y > Z$
C) $Z > Y > X$
D) $Y > Z > X$
Explanation
(c)
[table] Symbols | K | L | M | N ; $\ _{19}X$ = | 2 | 8 | 8 | 1 ; $\ _{21}Y$ = | 2 | 8 | 9 | 2 ; $\ _{25}Z$ = | 2 | 8 | 13 | 2 [/table]
Hence, the order of number of electrons in $M$ shell is
$Z > Y > X$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.