Heat and Mass Transfer
Depending on the radiating properties, a body will be black when(Where a = absorptivity, p = reflectivity, X = transmissivity.)

P = 0, x = 1 and a = 0
X = 0, a + p = 0
P = 0, x = 0 and a = 1
P= 1, T = 0 and a = 0

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Heat and Mass Transfer
Kirchhoff's law states that

None of these
The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body
The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature
The wave length corresponding to the maximum energy is proportional to the absolute temperature

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