Assertion(A): Zinc displaces copper and silver from solutions of their salts. Reason (R): Zinc has a lower oxidation potential than copper and silver.

1. Basics of Displacement Reactions (basic)

In the world of chemistry, a displacement reaction is essentially a "power struggle" between elements. It occurs when a more reactive element displaces (or kicks out) a less reactive element from its compound. Think of it like a stronger athlete taking the seat of a weaker one in a game of musical chairs. As noted in Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.11, this reaction is a fundamental way to understand how different substances interact based on their chemical "strength" or reactivity.

The classic example often observed in laboratories involves an iron nail placed in a blue copper sulphate solution. Over time, the blue color of the solution fades, and the iron nail becomes coated with a brownish layer of copper. This happens because iron (Fe) is more reactive than copper (Cu). The iron essentially pushes the copper out of the sulphate bond to form iron sulphate (FeSO₄), leaving the copper as a solid metal: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s). If you were to try the reverse—putting copper into an iron sulphate solution—nothing would happen because copper isn't "strong" enough to displace iron (Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.45).

To predict whether a displacement reaction will occur, chemists look at the Reactivity Series. Metals like Zinc (Zn) and Lead (Pb) are higher up on this list than copper, meaning they can easily displace copper from its compounds (Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.11). This principle is not just a theoretical exercise; it is vital in industrial processes, such as the refining of silver, where copper metal is used to recover silver from silver nitrate solutions (Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.16).

Sources: Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.11; Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.16; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.45

2. The Reactivity (Activity) Series of Metals (basic)

At its core, the Reactivity Series (also known as the Activity Series) is a ranking of metals based on their "chemical personality." Some metals are naturally aggressive—they want to react with everything they touch—while others are noble and prefer to stay alone. By arranging metals in order of their decreasing reactivity, we create a roadmap that helps us predict how they will behave in chemical reactions Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.55.

This hierarchy is determined by a metal's ability to lose electrons and form positive ions. The easier it is for a metal to give up its electrons (oxidation), the higher it sits in the series. For example, Potassium (K) and Sodium (Na) are so reactive that they react violently even with cold water, whereas Gold (Au) and Silver (Ag) are so stable they are found in their pure, "free" state in the earth's crust Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.49.

A crucial rule to remember is the Displacement Principle: a metal higher in the series is "stronger" and can physically displace a metal lower in the series from its salt solution. For instance, if you drop a piece of Zinc into a Copper Sulphate solution, the Zinc will kick the Copper out to form Zinc Sulphate. Furthermore, Hydrogen [H] is often included in this series as a benchmark; metals positioned above hydrogen can displace it from dilute acids to produce hydrogen gas Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.55.

Sources: Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.45; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.49; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.55

3. Foundations of Redox Reactions (intermediate)

At its heart, a Redox reaction (short for Reduction-Oxidation) is a chemical process involving the transfer of electrons between two substances. While early chemistry defined oxidation simply as the gain of oxygen, the modern Electronic Concept provides a much more powerful lens: Oxidation is the loss of electrons, while Reduction is the gain of electrons Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.12. Because electrons cannot exist freely in a solution, these two processes always occur simultaneously—one species gives up electrons (getting oxidized) while another species accepts them (getting reduced).

To understand which metal will displace another in a reaction, we look at their reactivity or electrode potentials. In a displacement reaction, a more reactive metal (like Zinc) acts as a reducing agent because it has a high tendency to lose electrons and undergo oxidation Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.51. This "eagerness" to lose electrons is measured as Oxidation Potential. A metal with a higher oxidation potential is a stronger reducing agent. Conversely, in the standard table of Reduction Potentials, these strong reducers have very negative values (e.g., Zinc is -0.76V), while less reactive metals like Copper have positive values (+0.34V), indicating they would rather gain electrons than lose them.

In the context of industrial applications, we use these principles to extract metals. For instance, highly reactive metals like Sodium or Aluminium are used as reducing agents to displace less reactive metals from their oxides Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.51. The hierarchy of this "electron-pushing" power is what defines the Activity Series of metals.

Sources: Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.12; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.51

4. Practical Application: Corrosion and Galvanization (intermediate)

Corrosion is a natural process where metals are gradually destroyed by chemical or electrochemical reactions with their environment—primarily oxygen, moisture, and acids. While we often use the word "rusting," that term is technically reserved for the corrosion of iron. When iron is exposed to moist air, it develops a flaky, reddish-brown coating known as rust (hydrated iron oxide, Fe₂O₃·xH₂O). Other metals also undergo corrosion, though the results look different: silver develops a black coating (silver sulfide) and copper acquires a greenish layer (basic copper carbonate) Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.13.

To prevent the immense economic and structural damage caused by corrosion, various protective methods are used. One of the most effective industrial techniques is Galvanization. This involves coating iron or steel with a thin, protective layer of Zinc (Zn). Unlike simple painting or oiling, which merely provide a physical barrier, galvanization offers sacrificial protection. Because Zinc is more reactive than iron in the activity series, it has a higher tendency to lose electrons (higher oxidation potential) Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.50.

The remarkable feature of galvanization is that the iron remains protected even if the Zinc coating is scratched or broken. In such a case, the Zinc acts as a sacrificial anode—it "sacrifices" itself by reacting with the environment instead of the iron underneath Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.54. This is a fundamental application of the Reactivity Series, where a more reactive metal (like Zinc) preferentially undergoes oxidation compared to a less reactive metal (like Iron, Copper, or Silver).

Sources: Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.13; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.50; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.54

5. Electrochemical Cells and Batteries (exam-level)

An electrochemical cell, specifically a Voltaic (or Galvanic) cell, is a device that converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two different metal plates called electrodes submerged in a conducting liquid known as an electrolyte Science VIII, Electricity: Magnetic and Heating Effects, p.55. The core principle driving this cell is the difference in chemical reactivity between the two metals. For instance, in a Zinc-Copper cell, Zinc acts as the negative terminal because it has a greater tendency to lose electrons compared to Copper Science VIII, Electricity: Magnetic and Heating Effects, p.56.

To understand why specific metals act as certain terminals, we look at the Reactivity Series. Metals like Magnesium and Zinc are higher in the series than Iron or Copper, meaning they are more "active" and lose electrons more easily Science X, Metals and Non-metals, p.44. This ability to displace other metals from their salt solutions is the foundation of cell potential Science X, Metals and Non-metals, p.46. In electrochemistry, we quantify this tendency using Electrode Potentials:

• Oxidation Potential: Measures the tendency of a species to lose electrons. A more reactive metal (like Zinc) has a higher oxidation potential.
• Reduction Potential: Measures the tendency to gain electrons. By international convention, we usually use Standard Reduction Potentials (SRP). A highly reactive metal has a more negative (lower) SRP.

When these two metals are connected, the metal with the higher oxidation potential (the more reactive one) undergoes oxidation at the Anode, releasing electrons into the circuit. These electrons flow toward the metal with the lower oxidation potential (the Cathode), where reduction occurs. This flow of electrons constitutes the electric current that powers our devices.

Sources: Science VIII, Electricity: Magnetic and Heating Effects, p.55; Science VIII, Electricity: Magnetic and Heating Effects, p.56; Science X, Metals and Non-metals, p.44; Science X, Metals and Non-metals, p.46

6. Electrode Potentials: Reduction vs. Oxidation (exam-level)

To understand how batteries work or why metals corrode, we must look at Electrode Potential. This is essentially a measure of the "pressure" or tendency of a chemical species to either lose or gain electrons. In every redox reaction, one substance is oxidized (loses electrons) while another is reduced (gains electrons) Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.12. While we often speak of metals being "reactive," electrochemistry gives us a precise numerical scale to rank this reactivity using two complementary terms: Reduction Potential and Oxidation Potential.

By international convention, we usually measure the Standard Reduction Potential (SRP). A substance with a positive SRP (like Silver or Copper) is like a magnet for electrons—it "wants" to be reduced. Conversely, a substance with a negative SRP (like Zinc) "hates" gaining electrons and would much rather give them away. Therefore, a more negative reduction potential directly translates to a higher oxidation potential. This is why highly reactive metals like Sodium or Aluminum act as powerful reducing agents; they have a high tendency to lose electrons and undergo oxidation Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.51.

When comparing two metals, the one with the higher oxidation potential (the more negative SRP) will always be the one that displaces the other from a solution. For instance, Zinc (SRP ≈ -0.76V) has a much higher oxidation potential than Copper (SRP ≈ +0.34V). Because Zinc is more "eager" to lose electrons, it will force its electrons onto Copper ions, causing the Zinc to dissolve and the Copper to deposit as a solid. In any electrochemical cell, the electrode with the higher oxidation potential serves as the Anode (the negative terminal), where oxidation occurs Science-Class VII, NCERT (Revised ed 2025), Electricity: Circuits and their Components, p.25.

Sources: Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.12; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.51; Science-Class VII, NCERT (Revised ed 2025), Electricity: Circuits and their Components, p.25

7. Solving the Original PYQ (exam-level)

This question perfectly synthesizes your recent study of the Reactivity Series and Electrochemical Potentials. To solve this, you must connect the physical observation of a displacement reaction to its underlying chemical cause. As you learned, Zinc is more electropositive than Copper and Silver; in the activity series, it sits higher, meaning it has a much greater tendency to lose electrons. This chemical 'push' is what allows Zinc to displace less reactive metals from their salt solutions, making Assertion (A) absolutely true. Think of it as a more energetic element pushing a weaker one out of its seat.

However, the trap lies in the technical terminology of the Reason (R). In electrochemistry, a metal that is more reactive and oxidizes more easily is said to have a higher oxidation potential (or conversely, a lower, more negative reduction potential). Since Zinc is more reactive than Copper and Silver, it possesses a higher oxidation potential, not a lower one. This subtle flip of words is a classic UPSC tactic to test if you truly understand the relationship between reactivity and potential values. Therefore, while the assertion describes a valid chemical phenomenon, the reason provides a factually incorrect scientific premise, leading us to Correct Answer: (C).

When tackling such questions, the most common pitfall is the confusion between Reduction Potential and Oxidation Potential. Many students recall that Zinc has a 'lower' value on the standard reduction potential scale (approx. -0.76V) and mistakenly mark Reason (R) as true. Always pause to verify which specific potential the question is referring to. Options (A) and (B) are the 'decoy' choices designed to catch those who understand the general trend of reactivity but stumble on the specific definitions found in NCERT Class 12 Chemistry. Success in UPSC Science and Tech requires this level of precision in conceptual vocabulary.