Q 12-12-132JEE MainJEE Main 2025 (4 Apr, Shift 1)Easy
Considering the Bohr model of hydrogen-like atoms, the ratio of the radius of the $5^{\text{th}}$ orbit of the electron in $\text{Li}^{2+}$ and $\text{He}^+$ is:
Answer: (D) $\dfrac23$
$r_n = a_0\dfrac{n^2}{Z}$. For the same $n$, $r \propto \dfrac1Z$:
$$\frac{r_{\text{Li}^{2+}}}{r_{\text{He}^+}} = \frac{Z_{\text{He}}}{Z_{\text{Li}}} = \frac23$$
Solution by Sreeraj P, M.Sc Physics