When hydrogen atom is in its first excited level, its radius is .... its ground state radius
Answer & explanation
Correct answer: option 4
$r \propto n^2$. For ground state n = 1 and for first excited state n = 2.
$\frac{r_2}{r_1} = \frac{2^2}{1^2} = 4$
$\Rightarrow r_2 = 4 r_1$