An electron in a hydrogen atom moves with a uniform speed in its stationary circular orbit of radius $5.3\times {10}^{-11} \mathrm{m}$. Find

(i) its speed and 

An electron in a hydrogen atom moves with a uniform speed in its stationary circular orbit of radius $5.3\times {10}^{-11} \mathrm{m}$. Find

(ii) energy in its ground state.

A doubly-ionized Lithium atom is hydrogen-like with an atomic number $3$.

(i) Find the wavelength of radiation required to excite the electron in ${\mathrm{Li}}^{++}$ from the first to the third Bohr orbit. The ionization energy of the hydrogen atom is $13.6\mathrm{eV}$. 

A doubly-ionized Lithium atom is hydrogen-like with an atomic number $3$.

How many spectral lines are observed in the emission of spectra of the above exciting system?