A standard hydrogen electrode has zero electrode potential because

this electrode potential is assumed to be zero.

The correct answer is option 2. this electrode potential is assumed to be zero.

The standard hydrogen electrode (SHE) has an assigned potential of zero volts by convention. This decision provides a reference point against which the electrode potentials of other half-cells can be measured. Here’s a more detailed explanation:

Reference Standard: In electrochemistry, it’s crucial to have a standard reference for measuring the electrode potentials of different half-reactions. The SHE serves as this universal reference.

Convention: By international agreement, the potential of the SHE is set to zero volts at standard conditions (298 K, 1 M concentration of H\(^+\) ions, and 1 atm pressure of H\(_2\) gas). This is a purely arbitrary choice, made to establish a common baseline.

Measurement: When measuring the electrode potential of another half-cell, the SHE is used as the counter electrode in an electrochemical cell. The measured potential difference is then attributed entirely to the other half-cell since the SHE is defined to be zero.

Neutral Choice: Hydrogen, being the simplest element with a single proton and electron, provides a neutral and simple baseline. Its properties make it a stable and consistent reference.

Therefore, the statement "this electrode potential is assumed to be zero" is correct because it’s a matter of convention to have a standard point of comparison in electrochemical measurements.