Calculate the radius of the fourth orbit of the $B^{4+}$ ion. (in $pm$)

Supposing the electron is present in the $4^{th}$ energy level of $H$ atom. When the electron returns to the ground state,the possible transitions would 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:

The ratio of the velocity of an electron in the second orbit of $He^{+}$ to the third orbit of $B^{4+}$ is:

In a hydrogen atom,the energy difference between the states $n = 2$ and $n = 3$ is $E \ eV$. The ionization energy of the $H$-atom is: (in $E$)

The frequency of radiation emitted when the electron falls from $n = 4$ to $n = 1$ in a hydrogen atom will be (Given $h = 6.625 \times 10^{-34} \, J s$):-