Chemistry · Electrochemistry · NEET
More negative E° means STRONGER reducing power. A reducing agent gives away electrons (gets oxidised). A very negative reduction potential means the metal does not want to stay reduced — it prefers to lose electrons. So it is a strong reducer. Example: K (E° = -2.93 V) is a much stronger reducing agent than Ag (E° = +0.80 V). Just remember: lower number = stronger reducer.
First, arrange the E° values from lowest (most negative) to highest (most positive). The lowest E° is the strongest reducing agent. Then just read the metals in that same order to get the decreasing order of reducing power. For NEET, sort the numbers, then copy the metal order. Do not add or reverse anything — the order of E° from low to high IS the order of reducing power from strong to weak.
Zinc has E° = -0.76 V and copper has E° = +0.34 V. Zinc's E° is more negative, so zinc is a stronger reducing agent (it gives electrons more easily). Zinc gives its electrons to Cu²⁺ and pushes copper out. Copper is a weaker reducer, so it cannot take electrons back from Zn²⁺. Rule: a metal displaces another metal ion only if its own E° is more negative (lower).
For metals, yes — they run in the same direction. A metal that is a strong reducing agent (very negative E°) is also very reactive; it reacts fast, loses electrons easily, and sits high in the activity series. So the order of reducing power of metals = the order of reactivity. K and Na are top (very reactive, strong reducers); Au and Ag are bottom (unreactive, weak reducers).
NCERT and NEET give you STANDARD REDUCTION potentials (E°). Use those. For reducing power: more negative reduction potential = stronger reducer. If instead you flip the sign to get oxidation potential, then more POSITIVE oxidation potential = stronger reducer. Both give the same answer. To avoid mistakes, stick with reduction potentials and remember: lowest reduction potential = best reducing agent.
The standard electrode potential (E°) values of Al³⁺/Al, Ag⁺/Ag, K⁺/K and Cr³⁺/Cr are -1.66 V, 0.80 V, -2.93 V and -0.74 V, respectively. The correct decreasing order of the reducing power of the metals is:
At 298 K, the standard electrode potentials of Cu²⁺/Cu, Zn²⁺/Zn, Fe²⁺/Fe and Ag⁺/Ag are 0.34 V, -0.76 V, -0.44 V and 0.80 V respectively. On the basis of standard electrode potential, predict which of the following reactions cannot occur:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a list of electrodes (metals and their ions) arranged in the order of their standard reduction potential (E°), usually from most negative at the top to most positive at the bottom.
The top end, with the most negative E° values (like Li, K, Na). These metals lose electrons most easily, so they are the strongest reducing agents and the most reactive.
NEET repeatedly asks you to order reducing power, decide if a metal can displace another, and predict if a reaction is feasible. All of these are answered directly by comparing E° values, so this one idea covers several question types.
Yes. The standard hydrogen electrode (SHE) is set at E° = 0.00 V. Metals above hydrogen (negative E°) can displace H₂ from acids; metals below it (positive E°, like Cu, Ag) cannot.
Yes. For non-metals and other couples, the more positive E° means a stronger oxidising agent (like F₂). But for the metal reactivity order asked in NEET, focus on the most negative E° being the best reducer.
