Which of the following is an example of an ideal black body?

The surface of a thermos flask is kept shiny because:

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 the absorptance and reflectance of a surface are $0.4$ and $0.6$ respectively,then:

The sun radiates electromagnetic energy at the rate of $3.9 \times 10^{26} \ W$. Its radius is $6.96 \times 10^8 \ m$. The intensity of sunlight at the solar surface will be (in $W/m^2$):

If between wavelength $\lambda$ and $\lambda + d\lambda$,$e_\lambda$ and $a_\lambda$ are the emissive and absorptive powers of a body,respectively,and $E_\lambda$ is the emissive power of a perfectly black body,then according to Kirchhoff's law,which of the following is true?