...(i) where, E = energy of photon (50 W), n = number of photon h= Planck's constant (6.63×10−34Js) c= speed of light (3×108m∕s) λ= wavelength of light (795×10−9m) E = 50 W = 50 J = energy of photon 50J=
n×6.63×10−34Js×3×108m∕s
795×10−9m
⇒ n=
50×795×10−9
6.63×10−34×3×108
=1998.49×1017=1.998×1020=2×1020 ∴x=2 ∴ Answer is 2.