The emission of electrons from a metal surface exposed rto light radaition of appropriate wavelength is called photoelectroic effect .The emmited electron are called photo=-weklectron work function of threshold energy may be defined as the minimum amount of energy required to ejercted electron from a most surface .According to Einstein Maximum kinetic energy of ejected electron = Aborbed energy - Work function `(1)/(2) mv_(max)^(2) = h(v) - h(v_(n)) = hv [(1)/(lambda) -0 (1)/(lambda_(n))]` Where `v_(n)` and `lambda_(0)` are thereshold frequency and threshold wavelength respectively Sopping potential : it is the miximum potential at which the photoelectric current becomes zero if `V_(0)` is the stopping potential `eV_(0) = h(v- v_(0))`The folloeing figure indicates the energy livels of a certain atom .When the system moves from `2E` level to E lvel a photon of wavelength `lambda` is emitted .The wavelength of the photon produced during the transition from level `4E//3` to level E is A. `(lambda)/(3)`B. `(3lambda)/(4)`C. `(4 lambda)/(3)`D. `3 lambda`