Which one among the following metals is more reactive than hydrogen?

1. Chemical Properties of Metals (basic)

When we look at metals, we often think of their physical strength or shine, but for a UPSC aspirant, the true character of a metal lies in its chemical behavior. Chemically, metals are electropositive elements, meaning they have a natural tendency to lose electrons and form positive ions. This "generosity" with electrons defines how they react with the world around them. For instance, when metals react with oxygen, they produce metal oxides, which are generally basic in nature—a key distinction from non-metals, which form acidic oxides Science-Class VII, The World of Metals and Non-metals, p.54.

One of the most revealing ways to test a metal's chemical personality is its reaction with water. This reaction produces a metal oxide and hydrogen gas (Metal + Water → Metal Oxide + H₂). If the metal oxide is soluble, it further dissolves to form a metal hydroxide Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.43. However, not all metals are equally "eager" to react. This variation allows us to rank them in a Reactivity Series, which is a vertical arrangement of metals in order of their decreasing reactivity. In this series, Hydrogen serves as a crucial reference point; metals placed above hydrogen can displace it from water or acids, while those below it cannot Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.45.

Metal Type	Reaction with Water	Example
Highly Reactive	React violently with cold water; highly exothermic (can catch fire).	Potassium (K), Sodium (Na)
Moderately Reactive	React less violently; may require hot water or steam.	Calcium (Ca), Magnesium (Mg), Iron (Fe)
Least Reactive	Do not react with water at all, even as steam.	Gold (Au), Silver (Ag), Copper (Cu)

Finally, understanding Redox Reactions (Reduction-Oxidation) is essential. When a metal reacts with oxygen, it is oxidised because it gains oxygen (or more fundamentally, loses electrons). Conversely, if a metal oxide loses oxygen to become a pure metal, it is reduced Science, class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.12. This cycle of gaining and losing oxygen/electrons is the engine behind many industrial processes, such as extracting pure metals from their ores.

Sources: Science-Class VII, The World of Metals and Non-metals, p.54; Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.43; Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.45; Science, class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.12

2. Displacement Reactions in Chemistry (basic)

In the world of chemistry, a displacement reaction is essentially a "chemical takeover." It occurs when a more reactive element displaces or kicks out a less reactive element from its compound. Think of it like a game of musical chairs where a stronger, more energetic player can easily take the seat of someone less active. In a general form, if Metal A is more reactive than Metal B, the reaction looks like this: Metal A + Salt solution of B → Salt solution of A + Metal B Science, Class X (NCERT 2025 ed.), Chapter 3, p.45.

A classic example often observed in laboratories involves an iron nail placed in a blue-colored copper sulphate (CuSO₄) solution. Over time, the blue color fades and the iron nail develops a brownish coating. This happens because iron, being more reactive, displaces the copper from the solution. The chemical equation for this is: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s). In this process, the iron replaces the copper to form iron sulphate, and the displaced copper settles on the nail Science, Class X (NCERT 2025 ed.), Chapter 1, p.11.

To predict whether a displacement reaction will occur, we use the reactivity series—a ranking of metals from most reactive to least reactive. Metals like Zinc (Zn) and Lead (Pb) are higher up the list than Copper (Cu), meaning they can easily displace copper from its compounds like copper chloride or copper sulphate Science, Class X (NCERT 2025 ed.), Chapter 1, p.11. However, the reverse is not true; a less reactive metal like silver cannot displace iron from an iron sulphate solution because it lacks the chemical "strength" to force the iron out.

Reactants	Will a reaction occur?	Reasoning
Zinc + Copper Sulphate	Yes	Zinc is more reactive than Copper.
Copper + Silver Nitrate	Yes	Copper is more reactive than Silver.
Silver + Iron Sulphate	No	Silver is less reactive than Iron.

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

3. Metallurgy and Reactivity Connection (intermediate)

In the world of chemistry, not all metals are created equal. Some are hyper-active, reacting violently with air or water, while others are so stable they remain untarnished for centuries. To make sense of this, scientists developed the Reactivity Series—a vertical arrangement of metals in decreasing order of their chemical activity. At the heart of this series is Hydrogen, which serves as a vital reference point. Metals positioned above hydrogen are more reactive and can displace it from acids or water, whereas those below it (like Gold or Silver) are chemically "noble" and less reactive Science, Class X, Chapter 3, p.45.

This hierarchy is the foundation of Metallurgy, the science of extracting metals from their ores. Because metal extraction is essentially a reduction process (the act of removing oxygen or adding electrons to a metal ion), the difficulty of the task depends entirely on where the metal sits in the series Science, Class X, Chapter 3, p.51. Metals with very low reactivity are often found in nature in their free state (native form). In contrast, highly reactive metals are so tightly bonded to other elements that they never occur alone in the earth's crust Science, Class X, Chapter 3, p.49.

We can categorize the extraction techniques into three distinct groups based on this reactivity:

Reactivity Level	Metals (Examples)	Primary Extraction Method
High Reactivity	K, Na, Ca, Mg, Al	Electrolytic Reduction: These metals have a higher affinity for oxygen than carbon does, so carbon cannot reduce them. We must use electricity to pull them apart Science, Class X, Chapter 3, p.52.
Medium Reactivity	Zn, Fe, Pb, Sn	Reduction with Carbon: Carbon (coke) is strong enough to "steal" the oxygen away from these metal oxides.
Low Reactivity	Cu, Hg, Ag, Au	Heating or Native State: Their oxides are unstable and can often be reduced to metal just by heating Science, Class X, Chapter 3, p.50.

Understanding this connection is crucial for any civil servant or scientist because it explains why our history moved from the Copper Age to the Iron Age and finally to the Aluminium Age—it tracks our technological ability to master increasingly difficult reduction processes.

Sources: Science, Class X, Metals and Non-metals, p.45; Science, Class X, Metals and Non-metals, p.49; Science, Class X, Metals and Non-metals, p.50; Science, Class X, Metals and Non-metals, p.51; Science, Class X, Metals and Non-metals, p.52

4. Corrosion and Sacrificial Protection (intermediate)

Corrosion is the natural process that converts a refined metal into a more chemically stable form, such as its oxide, hydroxide, or sulfide. It is essentially the environmental "eating away" of metals when they are attacked by substances like moisture, acids, and gases in the atmosphere. While we often focus on iron, many metals undergo this process. For instance, silver articles turn black because they react with sulfur in the air to form silver sulfide (Ag₂S), and copper develops a green coating of basic copper carbonate when exposed to moist carbon dioxide Science, Class X, Metals and Non-metals, p.53. For iron, the result is the familiar reddish-brown flaky substance we call rust, which is chemically hydrated ferric oxide (Fe₂O₃·xH₂O).

To prevent this degradation, we use various methods like painting, oiling, or alloying. However, one of the most sophisticated chemical techniques is Sacrificial Protection. In this method, a more reactive metal is used to "sacrifice" itself to save the primary metal. The most common example is Galvanisation, where iron or steel is coated with a thin layer of Zinc Science, Class X, Metals and Non-metals, p.54. Because Zinc is more reactive than Iron, it oxidizes (loses electrons) more readily. Interestingly, even if the Zinc coating is scratched or broken, the iron remains protected because the Zinc continues to react preferentially with the environment, acting as a "sacrificial anode."

The following table summarizes how different common metals respond to environmental exposure:

Metal	Corrosion Product	Appearance
Iron	Hydrated Ferric Oxide (Rust)	Reddish-brown flakes
Silver	Silver Sulfide (Ag₂S)	Black tarnish
Copper	Basic Copper Carbonate	Green coating

Understanding these principles is vital for infrastructure management. In large ships or underground pipelines, blocks of magnesium or zinc are often bolted to the iron structures. These blocks corrode away over time, protecting the vital steel structure from the harsh salt water or moist soil—a perfect real-world application of the reactivity series in action.

Sources: Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.53; Science, Class X (NCERT 2025 ed.), Metals and Non-metals, p.54; Science, Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.13

5. The Reactivity (Activity) Series (exam-level)

In the study of chemistry, not all metals are created equal. Some, like Potassium, are so chemically "aggressive" that they react violently with water, while others, like Gold, are so stable they remain untarnished for centuries. To organize this behavior, scientists developed the Reactivity Series (or Activity Series) — a list of metals arranged in the order of their decreasing chemical activities Science, Class X (NCERT 2025 ed.), Chapter 3, p.45.

At the heart of this series is a metal's ability to lose electrons and form positive ions. The more easily an atom gives up its electrons, the more reactive it is. Interestingly, although Hydrogen is a non-metal, it is included in this series as a crucial reference point. It serves as the "dividing line": metals positioned above Hydrogen are reactive enough to displace it from dilute acids or water, whereas those below it are generally unreactive with acids Science, Class X (NCERT 2025 ed.), Chapter 3, p.55.

One of the most practical applications of this concept is the Displacement Reaction. A more reactive metal (higher in the series) has the power to "push out" or displace a less reactive metal from its salt solution. For example, if you place a Zinc strip in a Copper(II) sulphate solution, the Zinc will displace the Copper because it sits higher in the series. This logic is fundamental to understanding metallurgy — the process of extracting metals from their ores — as less reactive metals are easier to extract than highly reactive ones Science, Class X (NCERT 2025 ed.), Chapter 3, p.55.

Reactivity Level	Metals	Behavior with Acids/Water
High	K, Na, Ca, Mg	React vigorously; displace Hydrogen easily.
Medium	Al, Zn, Fe, Pb, [H]	React moderately; Hydrogen is the benchmark.
Low	Cu, Hg, Ag, Au	Very stable; do not displace Hydrogen from acids.

Sources: Science, Class X (NCERT 2025 ed.), Chapter 3: Metals and Non-metals, p.45; Science, Class X (NCERT 2025 ed.), Chapter 3: Metals and Non-metals, p.55

6. Hydrogen as a Reference in Reactivity (exam-level)

In the study of chemistry, the Reactivity Series (or Activity Series) is a vital tool that ranks metals based on their chemical vigor—specifically, their ability to lose electrons and form positive ions. While this list primarily features metals, Hydrogen serves as the crucial reference point or 'benchmark' in the middle of the series Science, Metals and Non-metals, p.45. Even though Hydrogen is a non-metal, it shares a unique characteristic with metals: the tendency to lose its valence electron to become a positive ion (H⁺). This allows chemists to compare the 'strength' of metals against a common standard.

The position of a metal relative to hydrogen tells us exactly how it will behave in a chemical reaction. Metals placed above hydrogen are more reactive than it. These 'active' metals—such as Potassium, Sodium, Zinc, and Tin (Sn)—have the power to displace hydrogen from dilute acids or water, releasing it as Hydrogen gas (H₂) Science, Acids, Bases and Salts, p.20. Conversely, metals placed below hydrogen are less reactive and lack the 'muscle' to push hydrogen out of its compounds. These include 'noble' metals like Copper (Cu), Mercury (Hg), Silver (Ag), and Gold (Au).

Understanding this hierarchy is essential for predicting whether a reaction will occur. For instance, if you drop a piece of Zinc into dilute Hydrochloric acid, you will see bubbles of H₂ gas because Zinc is above Hydrogen. However, if you drop a Silver coin into the same acid, no reaction will occur because Silver is below Hydrogen in the series Science, Metals and Non-metals, p.55. This fundamental principle helps us understand why some metals corrode easily while others remain shiny and pure in nature.

Category	Metals	Reaction with Dilute Acids
Above Hydrogen	K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb	Displace Hydrogen to form H₂ gas
Reference Point	Hydrogen (H)	N/A
Below Hydrogen	Cu, Hg, Ag, Au, Pt	Do not displace Hydrogen

Sources: Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.45; Science, class X (NCERT 2025 ed.), Metals and Non-metals, p.55; Science, class X (NCERT 2025 ed.), Acids, Bases and Salts, p.20

7. Solving the Original PYQ (exam-level)

Now that you have mastered the reactivity series, this question serves as a perfect test of your ability to visualize the chemical "hierarchy." You have learned that metals are ranked based on their ease of losing electrons to form positive ions, and in this hierarchy, Hydrogen acts as the vital benchmark. Any metal positioned above it is reactive enough to displace hydrogen from dilute acids, while those below it are too stable to do so. According to Science, class X (NCERT), this concept is the fundamental building block for understanding displacement reactions and metal extraction.

To arrive at the correct answer, visualize the vertical arrangement of the series in your mind. You will recall that Tin (Sn) sits in the middle section of the activity series, positioned comfortably above hydrogen along with metals like Iron and Lead. This makes Tin (D) the only metal in the given list capable of displacing hydrogen. On the other hand, Mercury, Copper, and Silver are all part of the low-reactivity group located below hydrogen. UPSC frequently uses these three as "traps" because they are common elements, yet they are chemically "lazy" and will not react with dilute acids to release hydrogen gas, making them incorrect choices in this context.