The correct option is A 1021
According to Planck's quantum theory, E=nhcλ
Where, E = energy of the radiation =600 W=600 J/s
n = number of photons emitted per second
h = Planck's constant =6.626×10−34 J s
c = speed of light =3×108 m/s
λ = wavelength of the radiation =331.3 nm=331.3×10−9m
On subtituting the values in the equation and solving for n,
n=Eλh.c=600×331.3×10−96.626×10−34×3×108
On solving n=1×1021 photons/second