Question

The radius of hydrogen atom in the ground state is $5.3\times {10}^{-11}m$. When struck by an electron, its radius is found to be $21.2\times {10}^{-11}m$. The principal quantum number of the final state will be

• A. $2$
• B. $3$
• C. $4$
• D. $16$

Answer 1

The correct option is B $3$

From the concept attached:
$r\propto n^2$
For $n=1$ if $r_1=5.3\times {10}^{-11}m$
Then, $r=21.4\times {10}^{-11}=4r_1=2^2{r}_1$ so $n=2$