Gamma rays (y-rays) are high-energy photons. In a certain nuclear reaction, a y-ray of energy 0.798 MeV (million electronvolts) is produced. Compute the frequency of such a photon.
0.798 MeV = 7.98 * 10^5 eV * 1.6022*10^-19 J/eV = 1.279*10^-13 J
Now recall that E = hf
so solve for f