Isothermal efficiency is defined as the ratio of the

(a) Isothermal work to the actual work, i.e., \(\eta_{\text {iso }}=\frac{W_{\text {iso }}}{W_{\text {actual }}}\)

(b) Actual work to the isothermal work, i.e., \(\eta_{\text {iso }}=\frac{W_{\text {actual }}}{W_{\text {iso }}}\)

(c) Actual work to the ideal work, i.e., \(\eta_{\text {iso }}=\frac{W_{\text {actual }}}{W_{\text {ideal }}}\)

(d) None of these.