Calculate the ratio of the radius of the $2^{nd}$ and $3^{rd}$ orbit of a hydrogen atom. (Note: $r_n \propto n^2$)

The radius of the electron in the first excited state of a hydrogen atom is:

What is the ratio of the velocity of an electron in the ground state of a hydrogen atom to the velocity of an electron in the second excited state of $He^{+}$?

The ratio of minimum wavelengths of Lyman and Balmer series will be $:-$

What is the energy (in $J$ atom$^{-1}$) required for the following process?
$Li^{2+}(g) \to Li^{3+}(g) + e^-$
(Take the ionization energy for the $H$ atom in the ground state as $2.18 \times 10^{-18}$ $J$ atom$^{-1}$)

Based on the equation $E = -2.178 \times 10^{-18} \ J \left( \frac{Z^2}{n^2} \right)$,certain conclusions are written. Which of them is not correct?