What does a negative \(E^o\) (standard electrode potential) value of a redox couple indicate?

Redox couple is a stronger reducing agent than couple \(H^+ / H_2\) couple

A negative standard electrode potential \((E^o)\) value of a redox couple indicates that the redox couple is a stronger reducing agent than the \(H^+/H_2\) couple.

The standard electrode potential is a measure of the tendency of a redox couple to undergo reduction. A more positive \(E^o\) value indicates a greater tendency to undergo reduction.

The \(H^+/H_2\) couple has a standard electrode potential of 0.00 V, so any redox couple with a negative \(E^o\) value is a stronger reducing agent than the \(H^+/H_2\) couple.

Here is an example:

\(Zn^{2+} + 2e^- \longrightarrow ZnS; E^o = -0.76V\)

The negative \(E^o\) value indicates that the \(Zn^{2+}/Zn\) couple is a stronger reducing agent than the \(H^+/H_2\) couple. This means that zinc will more readily donate electrons to another species than hydrogen will.

Therefore, the correct answer is 1. Redox couple is a stronger reducing agent than the \(H^+/H_2\) couple.