Could someone please explain

Microwave can cause rotaional mption in the molecules.IR can give vibrational and UV -Vis can excite electrons .X rays and gamma rays can cause bond breaking.

E = hv ( a photon)
v is the frequency and v= c* wavelength
E =hc/ wavelength
wavelength is given in question in cm so convert it in m.c and h values will be given and plug in the equation to know E in J.
Total energy given by oven in 1 minute = 850J /s * 60 s
Number of photons = E (total)/ E( one photon in b part of question)
Moles of photons = number of photons * 1 mole / avogadro's number.