[" A "5" W source emits monochromatic light of wavelength "],[5000" A.When placed "0.5m" away,it liberates "],[" photoelectrons from a photosensitive metallic surface "],[" When the source is moved to a distance of "1.0m" ,the "],[" number of photoelectrons liberated will be reduced by a "],[" factor of "],[[" (a) "4," (b) "8," (c) "16," (d) "2]]