The radius of the first Bohr orbit for hydrogen is $0.53 \ \mathring{A}$. The radius of the third Bohr orbit would be .............. $\mathring{A}$.

If '$X$' is the ionization energy of hydrogen,then the energy required for the excitation of a $Li^{2+}$ electron from the $2^{nd}$ excited state to the $5^{th}$ excited state is:

Which one of the following is not the characteristic of Planck's quantum theory of radiation?

Find the energy of a photon having a wavelength of $6000 \ \mathring{A}$. (Given: $h = 6.62 \times 10^{-27} \ erg \cdot s$)

The ionization energy of an electron in an excited state of a hydrogen atom is $+0.85 \, eV$. What will be the energy of the emitted photon in $eV$ when it returns to the ground state?

The energy associated with the first orbit of $He^{+}$ is