Q. Radius of the first excited state of Helium ion is given as : $a_0\to$ radius of first stationary state of hydrogen atom.
A) $r=4a_0$
B) $r=2a_0$
C) $r=\frac{a_0}{2}$
D) $r=\frac{a_0}{4}$
Explanation
[Solution by Dr. Abubacker] $r=a_0\frac{n^2}{Z}$. For He⁺ ($Z=2$) the first excited state has $n=2$, so $r=a_0\cdot\frac42=2a_0$. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.