A laser emits a beam of light of $2mm$ diameter. If the power of beam is $10mW$, the intensity of the beam of light is

Question

$\begin {array} {1 1} (a)\;31.8 \times 10^3W/m^2 & \quad (b)\;3.18 \times 10^3W/m^2 \\ (c)\;31.8 \times 10^5W/m^2 & \quad (d)\;3.18 \times 10^5W/m^2 \end {array}$