If $E$ Represents emissivity of a substance ,$E_b$ Represents emissivity of black body and $a$ Represents coefficient of absorption, then correct equation out of the following is

Ratio of emissive power and absorptive power of all substances is equal to the emissive power of black body under the same condition. This law is

An ideal black-body at room temperature is thrown into a furnace. It is observed that

A black pattern on a porcelain bowl appears brighter than the rest of bowl, when it is strongly heated and taken to a dark room. This is an illustration of