The four lowest energy levels of the $H$ atom are shown in the figure. The number of emission lines will be ...... .

The emission spectrum of hydrogen discovered first and the region of the electromagnetic spectrum in which it belongs, respectively, are

Quantum theory was postulated by :

For a hydrogen atom,the energy difference between the first and second Bohr orbits is $3B/4$. What is the energy difference between the first and third Bohr orbits?

The energies of an electron in the first orbit of $He^{+}$ and in the third orbit of $Li^{2+}$ in $J$ are respectively:

The kinetic energy of an electron in the second Bohr orbit of a hydrogen atom is equal to $\frac{h^{2}}{xma_{0}^{2}}$. The value of $10x$ is ........ . ($a_{0}$ is radius of Bohr's orbit) (Nearest integer) [Given : $\pi=3.14$]