The radius of the first orbit of $Li^{2+}$ is $X \mathring{A}$. The radius of the third orbit of $He^{+}$ (in $\mathring{A}$) is (in $X$)

Assertion : Angular momentum of an electron in any orbit is given by angular momentum $= \frac{nh}{2\pi}$,where $n$ is the principal quantum number.
Reason : The principal quantum number,$n$,can have any integral value.

If the electron of a hydrogen atom is in the third orbit,it represents its ...... excited state.

The energy required to excite an electron in a hydrogen atom from the ground state $(n=1)$ to the first excited state $(n=2)$ is $..........$ $eV$.

The ground state energy of hydrogen atom is $-13.6 \ eV$. The energy of the second excited state of $He^{+}$ ion in $eV$ is:

The value of Planck's constant is $6.63 \times 10^{-34} \, J \cdot s$ and the speed of light is $3.0 \times 10^8 \, m \cdot s^{-1}$. The wavelength of a quantum of light with a frequency of $8 \times 10^{15} \, s^{-1}$ is closest to which of the following values in meters?