In $He^{+}$ ion,the energy of $2^{nd}$ orbit is $-13.6 \ eV/atom$. The kinetic energy of the same orbit for $He^{+}$ ion will be:

If a hydrogen atom is excited by an energy of $8.4 \ eV$,what will be the number of spectral lines emitted?

Assertion $:-$ Emitted radiation will fall in the visible region when an electron jumps from $n=4$ to $n=2$ in a hydrogen atom.
Reason $:-$ The frequency of radiation of the Lyman series belongs to the visible region for a hydrogen atom.

The expression for Bohr's radius of an atom is

In the hydrogen spectrum,a line corresponds to a transition from the $3^{rd}$ to the $5^{th}$ orbit. Identify the series to which this transition belongs.

The energy of the electron in the first orbit of $He^{+}$ is $-871.6 \times 10^{-20} \ J$. The energy of the electron in the first orbit of hydrogen would be