An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength so emitted illuminates a photo-sensitive material having work function 2.75 eV. If the stopping potential of the photo-electron is 10V,the value of n is
Difference of 4 and 1 energy level is 12.75 eV. So, higher energy level is 4 to ground and excited state is n=3.