The ratio of the velocity of an electron in the ground state of a hydrogen atom to its velocity in the second excited state of a $He^{+}$ ion is:

Observe the following statements:
Statement-$I$: Rutherford model of an atom cannot explain the stability of an atom.
Statement-$II$: The wavelength of $X$-rays is higher than the wavelength of microwaves.
The correct answer is:

What will be the frequency of the radiation emitted when an electron in a hydrogen atom jumps from $n = 4$ to $n = 1$? $(h = 6.625 \times 10^{-34} \,J \cdot s)$

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

The energy of the second Bohr orbit of the hydrogen atom is $-328 \ kJ \ mol^{-1}$. Hence,the energy of the fourth Bohr orbit would be .............. $kJ \ mol^{-1}$.

The radius of a hydrogen atom in its ground state is $0.53 \ \mathring{A}$. The radius of the $Li^{2+}$ ion in the same state (atomic number = $3$) is ............. $\mathring{A}$.