What is the emissivity of a black body ?

ANS:A - 1

The emissivity of a black body is 1. A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. It also emits radiation at all frequencies with maximum possible intensity at any given temperature. The emissivity of a black body is defined as 1, indicating that it emits radiation at the maximum possible rate for a given temperature.