For athermanous substances,the coefficient of transmission is

The coefficient of absorption $(a)$ and the coefficient of reflection $(r)$ of a thin uniform plate are $0.77$ and $0.17$ respectively. If $250 \ kcal$ of heat is incident on the surface of the plate,the quantity of heat transmitted $(t)$ is: (in $kcal$)

Which of the following statements is correct?

$Assertion :$ $A$ 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.

$A$ sphere,a cube,and a thin circular plate,all made of the same material and having the same mass,are initially heated to a temperature of $1000^{\circ}C$. Which one of these will cool first?

Compared to a white-skinned person,what does a dark-skinned person experience?