What is standard hydrogen electrode ? Give the reaction that occurs at this electrode when it acts as a positive electrode in an electrochemical cell.

Explanation

(a). It is the reference electrode, in which hydrogen gas at 1 bar pressure is passed in to 1 M HCl at 298 K in which a foil of platinum coated with platinum black remains immersed.
(b). `2H^(+)(aq)+2e^(-)toH_(2)(g)` is reaction taking place, when it acts as positive electrode.