Answer
$4.8\times 10^6\frac{J}{mol}$
Work Step by Step
We know that
$E=\frac{hc}{\lambda}$
We plug in the known values to obtain:
$E=\frac{6.63\times 10^{-34}\times 3\times 10^8}{25nm\times \frac{1}{1\times 10^9nm}}=8.0\times 10^{-18}\frac{J}{photon}$
We can convert the energy into $\frac{J}{mol}$ as follows:
$E=8.0\times 10^{-18}\frac{J}{photon}\times \frac{6.02\times 10^{23}photons}{mol}=4.8\times 10^6\frac{J}{mol}$