Question

In a device, the complete conversion of heat energy into mechanical work------.
(A) is not possible at any cost
(B) depends on the type of device in use
(C) depends on the atmospheric temperature, pressure etc.
(D) depends on the type of fuel used

Answer 1

The processes that involve the transfer or conversion of heat energy are irreversible. There is a natural tendency of any isolated system to degenerate into a more disordered state.

Complete step by step answer:
The second law of thermodynamics. The Kelvin-Planck statement or the heat engine statement of the second law of thermodynamics states that it is impossible to devise a cyclically operating deice3, the solar effect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work. This implies that it is impossible to build a heat engine that has $100\%$ thermal efficiency.
In a device, the complete conversion of heat energy into mechanical work is not possible at any cost.

So, the correct answer is “Option A”.

Note:
Carnot’s cycle is reversible and thus represents the upper limit on efficiency of an engine cycle. Practical engine cycle is irreversible and thus have inherently lower efficiency than the Carnot efficiency when operated between the same temperatures one of the factors determining efficiency is how heat is added to the working field in the cycle achieves maximum efficiency because all the heat is added to the working filled at the maximum temperature and removed at the minimum temperature.