For a hydrogen atom,the energy of an electron in the first excited state is $-3.4 \ eV$. The kinetic energy $(KE)$ of the same electron in the hydrogen atom is $x \ eV$. The value of $x$ is . . . . . . $\times 10^{-1} \ eV$. (Nearest integer)

Calculate the ionization energy of $H$,$He^{+}$,and $Li^{2+}$ in $kJ \, mol^{-1}$.

What is the maximum wavelength in the Lyman series of $He^{+}$ ion?

What will be the number of photons required to obtain $1 \ J$ of energy by radiation having a wavelength of $4000 \ \mathring{A}$?

Consider an electron moving in the first Bohr orbit of a $He^{+}$ ion with a velocity $v_1$. If it is allowed to move in the third Bohr orbit with a velocity $v_3$, then indicate the correct $v_3: v_1$ ratio.

The electron energy in a hydrogen atom is given by $E_n = (-2.18 \times 10^{-18})/n^2 \ J$. Calculate the energy required to remove an electron completely from the $n = 2$ orbit. What is the longest wavelength of light in $cm$ that can be used to cause this transition?