Energy of a stationary electron in the hydrogen atom is $$E=\frac{13.6}{n^2} \mathrm{~eV}$$, then the energies required to excite the electron in hydrogen atom to (a) its second excited state and (b) ionised state, respectively.

The graph of $$\ln \left(\frac{R}{R_0}\right)$$ versus $\ln A$ is where $$R$$ is radius of a nucleus, $$A$$ is its mass number, and $$R_0$$ is constant

The shortest wavelength of X-rays emitted from an X-ray tube depends upon ........... .

The wavelength of the first spectral line of the Lyman series of hydrogen spectrum is