The energy required to excite an electron in a $H$ atom from the first orbit to the second orbit is ......

Which of the following electronic transitions in a hydrogen atom results in the emission of a spectral line with the shortest wavelength?

The total energy of the electron of $H$ atom in the second quantum state is $-E_2$. The total energy of the $He^{+}$ ion in the third quantum state is

The radii of two of the first four Bohr’s orbits of the hydrogen atom are in the ratio $1 : 4$. The energy difference between them may be

The correct representation of the wavelength-intensity relationship of an ideal black body radiation at two different temperatures $T_{1}$ and $T_{2}$ (where $T_{2} > T_{1}$) is:

What is the maximum number of different spectral lines obtained when a sample of a large number of $H$-atoms in the $5^{th}$ excited state makes transitions to the ground state,given that no lines are emitted in the Balmer series?