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(D) According to Stefan-Boltzmann Law,the rate of heat loss $dQ/dt$ is proportional to the surface area $A$ for a given temperature $T$ and environmen

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$2:1$

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(D) According to Stefan-Boltzmann Law,the rate of heat loss $dQ/dt$ is proportional to the surface area $A$ for a given temperature $T$ and environment temperature $T_0$,i.e.,$dQ/dt \propto A(T^4 - T_0^4)$.Since the rate of cooling $R = (dQ/dt) / (ms)$,where $m$ is mass and $s$ is specific heat,and both are the same for the sphere and the disc,the ratio of the rate of cooling is equal to the ratio of their surface areas.Surface area of a sphere $A_s = 4\pi r^2$.Surface area of a disc (considering both sides) $A_d = 2 	imes (\pi r^2) = 2\pi r^2$.Therefore,the ratio of the rate of cooling is $\frac{R_s}{R_d} = \frac{A_s}{A_d} = \frac{4\pi r^2}{2\pi r^2} = \frac{2}{1}$.

If the initial temperatures of a metallic sphere and a disc,of the same mass,radius,and material,are equal,then the ratio of their rate of cooling in the same environment will be:

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