$($ii$)$ A Carnot heat engine operates with a source a temperature $T_1$ and a sink at

temperature $T_2.T_1$ and $T_2$ can vary between $30K$ and $1000K,$ but $T_1-T_2$ is always

fixed at $100K.$ The highest possible efficiencys such a Carnot engine is

a$.0\mathrm{.}66$

b$.0\mathrm{.}33$

$\mathrm{.}0\mathrm{.}25$

d$.0\mathrm{.}10$