For athermanous substances,the coefficient of transmission is

$A$ certain substance emits only the wavelengths ${\lambda _1}, {\lambda _2}, {\lambda _3}$ and ${\lambda _4}$ when it is at a high temperature. When this substance is at a colder temperature,it will absorb only the following wavelengths:

We consider the radiation emitted by the human body. Which of the following statements is true?

$A$ perfect black body is ........

According to Kirchhoff's law,the ratio of emissive power to absorptive power for all bodies is:

$Assertion :$ $A$ body that is a good radiator is also a good absorber of radiation at a given wavelength.
$Reason :$ According to Kirchhoff's law,the absorptivity of a body is equal to its emissivity at a given wavelength.