How many emission spectral lines are possible when a hydrogen atom is excited to the $n$th energy level?

Which of the following transitions has the minimum wavelength?

Energy of an electron in the ground state of the hydrogen atom is $-2.18 \times 10^{-18} \ J$. Calculate the ionization enthalpy of atomic hydrogen in terms of $J \ mol^{-1}$.

Which observations are not explained by the electromagnetic theory of physics?

The difference in wavelength of first and second spectral lines of Lyman series in $Li^{2+}$ ion spectrum is ................ $\mathring{A}$

In a hydrogen atom,the energy of an $e^-$ in an orbital is given by $E = \frac{-constant}{n^2} \ (kJ \ mol^{-1})$. Which of the following properties is constant according to the given equation?