What is the wavelength of light required to raise an electron in the $O^{7+}$ ion from $n=1$ shell to $n=2$ shell in $nm$?

What is the wave number of a photon emitted during the transition from orbit $n=4$ to $n=2$ in a hydrogen atom (in $cm^{-1}$)? $[R_{H}=109677 \ cm^{-1}]$

The ratio of the time period of an electron in the first and third orbit of an $H$-atom would be:

The Ritz combination principle states that:

The wavelength of a spectral line emitted by a hydrogen atom in the Lyman series is $\frac{16}{15 R} \ cm$. What is the value of $n_2$? $(R = \text{Rydberg constant})$

Which of the following graphs correctly represents the variation of Kinetic Energy $(K.E.)$ of an electron in a Bohr orbit with respect to the principal quantum number $(n)$?