What is the ratio of the radii of the second orbit for $H$,$He^{+}$,and $Li^{2+}$?

The frequency of radiation absorbed or emitted when transition occurs between two stationary states with energies $E_1$ (lower) and $E_2$ (higher) is given by

The wavelength and frequency of a photon with energy $2 \ eV$ are respectively:

When an electron jumps from a lower to a higher orbit,its energy

The shortest wavelength of $He^{+}$ ion in Balmer series is $x$. Then,the longest wavelength in the Paschen series of $Li^{2+}$ is:

The value of Planck's constant is $6.63 \times 10^{-34} \ J \ s$. The speed of light is $3 \times 10^{17} \ nm \ s^{-1}$. Which value is closest to the wavelength in nanometers of a quantum of light with a frequency of $6 \times 10^{18} \ s^{-1}$?