The magnitude of kinetic energy $(K.E.)$ of an electron in a Bohr orbit is equal to which of the following?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$:
Assertion $A$: In the photoelectric effect,the electrons are ejected from the metal surface as soon as the beam of light of frequency greater than threshold frequency strikes the surface.
Reason $R$: When the photon of any energy strikes an electron in the atom,transfer of energy from the photon to the electron takes place.
In the light of the above statements,choose the most appropriate answer from the options given below:

The ionization energy of a hydrogen atom is $-13.6 \ eV$. The energy required to excite an electron from the ground state to the first excited state is ...... (Avogadro number = $6.022 \times 10^{23}$)

Calculate the energy of an electron in the first four orbits of a hydrogen atom in $kJ \, mol^{-1}$ (Given: $N_A = 6.02 \times 10^{23} \, mol^{-1}$,Rydberg constant $R_H = 2.18 \times 10^{-18} \, J$).

The radii of the first Bohr orbit of $H$ $(r_{H})$,$He^{+}$ $(r_{He^{+}})$ and $Li^{2+}$ $(r_{Li^{2+}})$ are in the order

What is the energy associated with the first orbit of $Li^{2+}$ $(R_{H} = 2.18 \times 10^{-18} \ J)$?