Answer:
A particle or packet of light.
Step-by-step explanation:
A photon essentially doesn't have a charge and thus can't be called an electron. So, option 1 is incorrect.
Photons are in fact packets of electromagnetic energy that light is made up of. So, option 2 is correct.
A photon is not a gaseous mass that indicates the preliminary stage in a star's growth and thus can't be a protostar. So, option 3 is incorrect.
Photons having different energies are constituents of the electromagnetic spectrum and thus a single photon can't be a spectrum. So, option 4 is incorrect.