Which will be the first emission line in the infrared region of the hydrogen atomic spectrum?

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.

If the ratio of energies of an electron in the excited states of $H$ and $Li^{2+}$ is $1: 9$,the radius ratio of the electron in the same excited states of $H$ and $Li^{2+}$ is

The energy of the electron at infinite distance from the nucleus in Bohr’s model is taken as:

Heat treatment of muscular pain involves radiation of wavelength of about $900 \ nm$. Which spectral line of $H$ atom is suitable for this purpose?
$[R_H = 1.097 \times 10^7 \ m^{-1}, \ h = 6.626 \times 10^{-34} \ J \cdot s, \ c = 3 \times 10^8 \ m/s]$

Newtonian mechanics is applicable to which objects and not applicable to which objects?