# A radio wave of intensity $I$ is reflected by a surface. The intensity $(I)$, if pressure exerted on the surface is $2 \times 10^{-8} N/m^2$ , will be:
$\begin {array} {1 1} (a)\; 3 N/m^2 & \quad (b)\;4 N/m^2 \\ (c)\;6 N/m^2 & \quad (d)\;7 N/m^2 \end {array}$