Answer
$I=1.3\times10^{-2}\frac{W}{m^2}$
Work Step by Step
We know that for an isotropic source intensity $'I'$ can be determined as follows: $I=\frac{P}{4{\pi}r^2}$
Putting the values
$I=\frac{1.0}{4(3.14)(2.5)^2}=0.013\frac{W}{m^2}$
or $I=1.3\times10^{-2}\frac{W}{m^2}$
