ANS:C - both (a) & (b)

A perfect black body is characterized by its ability to absorb all incident radiation that falls upon it, regardless of wavelength or angle of incidence. This property makes it a perfect absorber of radiation. No radiation is reflected or transmitted; instead, all of it is absorbed. Simultaneously, a perfect black body is also a perfect emitter of radiation. According to Kirchhoff's law of thermal radiation, which applies to black bodies, the emissivity of a body (its effectiveness in emitting radiation) is equal to its absorptivity (its effectiveness in absorbing radiation). Since a perfect black body absorbs all incident radiation, it also emits radiation with maximum efficiency at all wavelengths and temperatures. Therefore, a perfect black body is both a perfect absorber and emitter of radiation, as described by the answer "both (a) & (b)".