A 100 W sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on him. The $\lambda$ of sodium light is 589 nm. At what rate are the photons delivered to the sphere ?

Question

$\begin {array} {1 1} (a)\;29.6 \times 10^{21} photon/s & \quad (b)\;2.96 \times 10^{20} photon/s \\ (c)\;0.296 \times 10^{20} photon/s & \quad (d)\;2.96 \times 10^{21} photon/s \end {array}$