The energy level diagram of $β^-$ emission from Cobalt is as shown. This diagram depicts the

emission of one $β^-$ particle and two gamma photons of different frequencies

The correct answer is Option (3) → emission of one $β^-$ particle and two gamma photons of different frequencies

Emission of one $β^-$ particle can be easily deduced by the diagram and two gamma photons of equal frequencies emitted because according to diagram energy gap between the two transitions seems almost equal and mass number cannot be changed by gamma photons also.