what is the energy per photon with diameter of 280 picometers? (1 picometer =1 * 10 (-12)?

Answer 1

Photons don't have diameters, they have wavelengths. If you meant that wavelength, I'm still not going to do your homework for you, but I'll tell you how to do it.

The energy of a photon of wavelength L is

E = L * c / h

where c is the speed of light and h is plank's constant

c = 3 x 10^8 m/sec
h = 6.6 x 10^-34 Joule-sec

Good luck.