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

Standard hydrogen electrode : It is a reference electrode against which the electrode potentials of all electrodes are measured.
When hydrogen gas at 1 atm-pressure is adsorbed over platinum electrode dipped in 1M HCl at `25^@C`, it is standard hydrogen electrode and its potential is, `E^@ = pm 0` volt.
A standard hydrogen electrode can be represented as : `Pt, H_2(g) " (1 atm)"/H^(+) " (1 mol) at " 25^@C`