For a perfectly black body, coefficient of emission is

Step-by-step solution

Perfect black body absorption and emission A perfectly black body absorbs all incident radiation regardless of wavelength, giving it an absorption coefficient a = 1 . Kirchhoff's law establishes that emissivity equals absorptivity at a given wavelength and temperature: e = a . Since a = 1 , the emissivity must also be unity: e = 1 . A perfectly black body is therefore both a perfect absorber and perfect emitter of radiation. The correct choice is B .