A typical $H2-O2$ PEMFC might operate at a voltage of $0\mathrm{.}65V$ and $=1\mathrm{.}15.$ At STP$,$

what is the efficiency of such a fuel cell $($use HHV and assume pure oxygen at the

cathode$)?(g_{H2O}=-237\mathrm{.}3\frac{kJ}{m}ol,h_{H2O}=-286\frac{kJ}{m}ol)(15$p$)$

a$.83\%$

b$.38\%$

c$.46\%$

d$.75\%$