Answer
See the answer below.
Work Step by Step
$c=\lambda\times\nu$
$\nu=2.998\times10^8\ m/s\div 540\times10^{-9}\ m=5.55\times10^{14}\ 1/s$
Per photon:
$E=h\times\nu$
$E=6.626\times10^{-34}\ J.s\times 5.55\times10^{14}\ 1/s=3.68\times10^{-19}\ J$
Per mole:
$E=4.85\times10^{-19}\ J\times6.022\times10^{23}\ 1/mol=221.5\ kJ/mol$
