Why is the standard reduction potential E, for the standard hydrogen electrode 0.00V?

Question

Please help me explain the reason why to this problem

Answer 1

Each electrode defines a half cell. Two half cells make up a complete electrochemical cell.
The assignment of 0.00 volts for the hydrogen electrode potential is arbitrary. It was chosen because it is easy to construct, it behaves in a consistent, reproducible manner, and it divides common electrode potentials into roughly equal numbers of positive and negative values.
The reason for assigning the reference value of zero to ONE electrode makes it possible to measure the potentials of other electrodes in a consistent way. They do that by constructing a complete electrochemical cell with two half cells, one of each is the hydrogen half cell. The voltage reading is the half cell potential of the OTHER electrode.