$\begin{array}{1 1}(a)\;\text{If }E^0_{Mn^+/M} \text{is -ve,}H^+\text{ will be reduced to }H_2\text{ by metal M}\\(b)\;\text{If }E^0_{Mn^+/M} \text{is +ve,}Mn^+\text{ will be reduced to }M\text{ by }H_2\\(c)\;\text{In a cell, }Mn^+/M\text{ assembly is attached to hydrogen half cell.To produce spontaneous cell reaction,metal M will act as negative electrode if the potential }Mn^+/M\text{ is negative.It will be serve as positive electrode,if }Mn^+/M\text {has a positive cell potential}\\(d)\;\text{Compounds of active metals (Zn,Na,Mg) are reducible by }H_2\text{ whereas those of noble metals(Cu,Ag,Au) are not reducible}\end{array}$
