Thermodynamics practice · Medium

Option B (${T_2} = 0K$) is correct because the efficiency of a Carnot engine is given by $\eta = 1 - \frac{T_2}{T_1}$, where $T_2$ is the temperature of the cold reservoir and $T_1$ is the temperature of the hot reservoir. For $\eta$ to be 100%, $T_2$ must be 0K.

Option A (External work done) is correct because in an isothermal process, the temperature remains constant, so the internal energy does not change, and all the heat added is converted into work.

Option C (Work) is correct because work is a process-dependent quantity, not a state variable. Temperature, pressure, and volume are state variables that describe the condition of the matter.

Option A is correct because the refrigerator transfers heat from its inside to the room, ultimately increasing the room's temperature, and this is due to heat flowing from a colder to a hotter region with external work.

Option B (840 J) is correct because it is the amount of heat calculated using the specific heat capacity of water, the mass, and the temperature change.

Option B ($\infty$) is correct because during a phase change (boiling), the temperature remains constant while heat is added, leading to an infinite specific heat.