(a) With the help of the \(\mathrm{T}-\mathrm{S}\) diagram, explain the working principle of a vapourcompression refrigeration system. Derive the expression for its C.O.P.

(b) An inventor claims to have developed an absorption refrigerating machine that receives heat from a source at \(125^{\circ} \mathrm{C}\), maintains the refrigerated space at \(-5^{\circ} \mathrm{C}\) and has a COP of 2. If the environment temperature is \(28^{\circ} \mathrm{C}\), can this claim be valid?

(c) "Natural refrigerant is the best choice towards replacement of CFCs." Justify the statement by explaining the desirable properties of a refrigerant.