Q. The electronic configuration of an element in ultimate and penultimate orbitals is $(n\ \ 1)s^{2}(n\ \ 1)p^{6}(n\ \ 1)d^{x}\ ns^{2}$. If $n\ \ 4\$and$\ x\ \ 5$ then number of protons in the nucleus is

A) 25
B) <724
C) 25
D) 30
Explanation

(c)
When $n = 4\ and\ x = 5$ then electronic configuration can be written as
$(4 - 1)s^{2}(4 - 1)p^{6}(4 - 1)d^{5}4s^{2}$
This electronic configuration represents Mn and its atomic number is 25. Hence, number of protons are 25 in its nucleus.

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.