According to Stefan's law, the total radiation from a black body per second per unit area is proportional to

The correct answer is Option D: T ⁴

Explanation: According to Stefan's law, also known as the Stefan-Boltzmann law, the total radiation emitted from a black body per second per unit area is proportional to the fourth power of the absolute temperature (T). Mathematically, this is expressed as E∝T ⁴, where E is the emissive power and T is the absolute temperature. Therefore, the correct exponent is 4, not any other value.