ANS:A - absorptivity = 1

For an ideal black body:

• Absorptivity (α) = 1: An ideal black body absorbs all incident radiation, so its absorptivity is 1.
• Reflectivity (ρ) = 0: An ideal black body does not reflect any incident radiation, so its reflectivity is 0.
• Emissivity (ε) = 1: An ideal black body emits radiation as per its temperature, following the Stefan-Boltzmann law, so its emissivity is 1.
• Transmissivity (τ) = 0: An ideal black body does not transmit any incident radiation through itself, so its transmissivity is 0.

• Absorptivity = 1
• Reflectivity = 0
• Emissivity = 1
• Transmissivity = 0