Which instrument is used to detect infrared rays?

$A$ body has a black spot on it. When the body is heated and taken into a dark room,the black spot glows more brightly. This can be explained by which of the following?

If $25\%$ of the total incident radiation $Q = 500 \, J$ is absorbed and $105 \, cal$ is transmitted,calculate the percentage of reflected power.

The temperature of the sun is measured with:

Three objects colored black,gray,and white can withstand hostile conditions up to $2800\,^oC$. These objects are thrown into a furnace where each of them attains a temperature of $2000\,^oC$. Which object will glow brightest?

If $150 \,J$ of energy is incident on an area of $2 \,m^{2}$. If $Q_{r}=15 \,J$ and the coefficient of absorption is $0.6$,then the amount of energy transmitted is: (in $\,J$)