What is emission power?

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$

A body of surface area $15\times {10}^{-3 }{\mathrm{m}}^2$ emits $0.3 \mathrm{kCal}$ in $40 \mathrm{s}$ at a temperature of ${70}^0 \mathrm{C}$. The emissive power of the surface at that temperature is

The temperature of bodies $X$ and $Y$ vary with time as shown in the figure. If emissivity of bodies $X$ and $Y$ are $e_{\mathit{X}}$ and $e_{\mathit{Y}}$ and absorptive powers are $A_{\mathit{X}}$ and $A_{\mathit{Y}}$, (assume other conditions are identical for both) then:

A polished metal plate, with a rough black spot on it, is heated to about $1400 \mathrm{K}$ and quickly taken to a dark room. The spot will appear,