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= 1, T = 0 and a = 0
P = 0, x = 0 and a = 1

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