$A$ perfectly black body is placed in an enclosure (furnace) at room temperature. Then:

Select the incorrect statement.

$A$ body is said to be opaque to the radiation if ($a$,$r$,and $t$ are the coefficients of absorption,reflection,and transmission,respectively).

Which of the following statements does not hold good for thermal radiation?

At a certain temperature for a given wavelength,the ratio of the emissive power of a body to the emissive power of a black body in the same circumstances is known as:

Two identical objects $A$ and $B$ are at temperatures $T_A$ and $T_B$ respectively. Both objects are placed in a room with perfectly absorbing walls maintained at temperature $T$ $(T_A > T > T_B)$. The objects $A$ and $B$ attain temperature $T$ eventually. Which one of the following is the correct statement?