In oxidation 1. Hydrogen is displaced from a substance. 2. an electropositive clement is added to or proportion of electropositive element increases in a substance. Select the correct answer using the code given below :

1. Basics of Chemical Reactions (basic)

Welcome to the first step of your journey into chemistry! To understand the world around us—from the rusting of an iron gate to the digestion of food—we must first distinguish between two fundamental types of changes: Physical and Chemical.

A physical change is essentially a change in the appearance or state of a substance (like shape or size) without altering its internal identity. For instance, when water freezes into ice, it is still H₂O; no new substance is formed (Science-Class VII, Changes Around Us: Physical and Chemical, p.59). In contrast, a chemical change results in the formation of entirely new substances with different properties. These changes occur through chemical reactions, which are governed by the Law of Conservation of Mass. This law dictates that mass can neither be created nor destroyed; therefore, the number of atoms for each element must remain identical before and after the reaction (Science, Class X, Chemical Reactions and Equations, p.3).

Feature	Physical Change	Chemical Change
New Substance	None formed	One or more new substances formed
Reversibility	Often reversible (e.g., melting ice)	Usually irreversible (e.g., burning wood)
Examples	Erosion, breaking glass	Combustion, rusting, cooking

One of the most vital concepts in chemical reactions is the dual process of Oxidation and Reduction. Classically, we define these by the movement of oxygen and hydrogen. Oxidation occurs when a substance gains oxygen or loses hydrogen. Conversely, Reduction involves the gain of hydrogen or the loss of oxygen. Interestingly, this definition extends to "electropositive" and "electronegative" elements: adding an electronegative element is oxidation, while adding an electropositive element (like a metal) is considered reduction (Science, Class X, Chemical Reactions and Equations, p.13-14).

Sources: Science-Class VII, Changes Around Us: Physical and Chemical, p.59, 68; Science, Class X, Chemical Reactions and Equations, p.3, 13-14

2. Electronic Nature: Electropositivity and Electronegativity (intermediate)

At the heart of every chemical interaction is the behavior of electrons. Elements are classified based on their 'electronic nature'—essentially, how much they 'love' or 'hate' their valence electrons. Electropositivity is the tendency of an atom to lose electrons and form positive ions (cations). This is the hallmark of metals. For instance, metals like Potassium (K) and Sodium (Na) have a very high urge to give away their outermost electron to achieve a stable electronic configuration Science, Class X (NCERT 2025 ed.), Chapter 3, p.55. This is why they sit at the top of the Activity Series; their high electropositivity makes them incredibly reactive Science, Class X (NCERT 2025 ed.), Chapter 3, p.45. Conversely, Electronegativity is the ability of an atom to attract electrons toward itself. Non-metals, such as Chlorine (Cl) or Oxygen (O), are highly electronegative. Instead of giving electrons away, they pull them in to form negative ions (anions). Understanding this tug-of-war is vital for the UPSC aspirant because it explains why certain elements react violently while others remain inert. In a chemical reaction, if an element is 'electropositive,' it acts as a donor, and if it is 'electronegative,' it acts as an acceptor.

Feature	Electropositivity	Electronegativity
Primary Nature	Metallic nature	Non-metallic nature
Electron Action	Tendency to lose electrons	Tendency to attract electrons
Ion Formed	Positive ion (Cation)	Negative ion (Anion)
Example	Potassium (K), Magnesium (Mg)	Fluorine (F), Oxygen (O)

In the context of chemical stability, elements with high electropositivity are easily 'oxidized' because they lose electrons readily. When we look at displacement reactions, a more reactive (more electropositive) metal will displace a less reactive metal from its salt solution, a principle that helps us arrange elements in the reactivity series Science, Class X (NCERT 2025 ed.), Chapter 3, p.46.

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

3. Classification of Chemical Reactions (basic)

Chemical reactions are the processes by which substances interact to form new products with different properties. To make sense of the vast array of chemical changes, we classify them based on how the atoms or ions rearrange themselves. At the most fundamental level, we look at whether substances are joining together, breaking apart, or swapping partners. For instance, a combination reaction occurs when two or more reactants join to form a single product, such as when hydrogen and chlorine gases combine to form hydrogen chloride (H₂ + Cl₂ → 2HCl) Science, Class X (NCERT 2025 ed.), Chapter 1, p.15. Conversely, a decomposition reaction is exactly the opposite: a single reactant breaks down into simpler products, often requiring energy in the form of heat, light, or electricity Science, Class X (NCERT 2025 ed.), Chapter 1, p.14.

Beyond simple joining and breaking, we observe "trading" behaviors. In a displacement reaction, a more reactive element kicks out a less reactive element from its compound. However, when two different compounds exchange their ions to form two new compounds, it is called a double displacement reaction. These often result in the formation of an insoluble solid called a precipitate, giving rise to precipitation reactions Science, Class X (NCERT 2025 ed.), Chapter 1, p.14. We also categorize reactions by their energy profile: exothermic reactions release heat (like respiration or burning natural gas), while endothermic reactions absorb energy from the surroundings Science, Class X (NCERT 2025 ed.), Chapter 1, p.15.

One of the most critical classifications for the UPSC is Redox reactions (Reduction-Oxidation). Classically, Oxidation is defined as the gain of oxygen or the loss of hydrogen. It also involves the removal of an electropositive element. On the other hand, Reduction involves the gain of hydrogen, the loss of oxygen, or the addition of an electropositive element Science, Class X (NCERT 2025 ed.), Chapter 1, p.14. In modern chemistry, we simplify this further: Oxidation is the loss of electrons (OIL: Oxidation Is Loss), and Reduction is the gain of electrons (RIG: Reduction Is Gain).

Common Reaction Types at a Glance:

Reaction Type	Core Mechanism	Example
Combination	A + B → AB	C + O₂ → CO₂
Decomposition	AB → A + B	CaCO₃ → CaO + CO₂
Displacement	A + BC → AC + B	Fe + CuSO₄ → FeSO₄ + Cu
Double Displacement	AB + CD → AD + CB	Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Sources: Science, Class X (NCERT 2025 ed.), Chapter 1: Chemical Reactions and Equations, p.14; Science, Class X (NCERT 2025 ed.), Chapter 1: Chemical Reactions and Equations, p.15; Science, Class X (NCERT 2025 ed.), Chapter 1: Chemical Reactions and Equations, p.9

4. Oxidation in Everyday Life: Corrosion and Rancidity (intermediate)

Oxidation is far more than just a chemical equation in a textbook; it is a persistent process that affects the world around us, from the structural integrity of bridges to the flavor of the food in our pantry. At its simplest, oxidation involves the addition of oxygen to a substance or the removal of hydrogen from it. In modern chemical terms, we also define it as the loss of electrons, which leads to an increase in the oxidation state of an element.

One of the most common manifestations of this process is corrosion. This occurs when a metal is attacked by substances in its environment, such as moisture, oxygen, or acids Science, Chapter 1, p.13. While we most frequently notice the rusting of iron—where it develops a reddish-brown flaky coating—other metals undergo similar transformations. For instance, silver develops a black coating of silver sulphide when exposed to air, and copper acquires a distinct green layer of basic copper carbonate due to its reaction with moist carbon dioxide Science, Chapter 3, p.53. To combat this, we use various prevention methods like galvanisation (coating iron with a thin layer of zinc), oiling, or creating alloys to enhance the metal's durability Science, Chapter 3, p.54.

Metal	Corrosion Product/Color	Chemical Cause
Iron	Reddish-brown (Rust)	Reaction with moist air
Silver	Black coating	Reaction with sulphur in air
Copper	Green coating	Reaction with moist CO₂

Another everyday example is rancidity, which specifically refers to the oxidation of fats and oils in food. When these substances are oxidised, their chemical structure changes, leading to an unpleasant smell and taste Science, Chapter 1, p.13. To prevent this, manufacturers often use antioxidants or flush food packaging (like chip bags) with nitrogen gas. Nitrogen acts as an inert atmosphere, displacing oxygen and ensuring the fats in the food do not react and spoil.

Sources: Science, Chapter 1: Chemical Reactions and Equations, p.13; Science, Chapter 3: Metals and Non-metals, p.53; Science, Chapter 3: Metals and Non-metals, p.54

5. Metallurgy: Reduction of Metal Ores (exam-level)

In the journey of extracting a metal from the earth, reduction is the most critical chemical bridge. Most metals exist in nature not as pure elements, but as compounds—usually oxides, sulphides, or carbonates. Since oxidation involves the addition of oxygen or the loss of electrons, reduction is the inverse: the removal of oxygen or the gain of electrons to restore the metal to its elemental state Science, Class X (NCERT 2025 ed.), Chapter 3, p.51.

Before reduction occurs, we must prepare the ore. It is chemically easier to obtain a metal from its oxide than from its sulphide or carbonate. Therefore, we use two primary pre-treatment methods based on the ore type:

Process	Target Ore	Conditions	Chemical Change
Roasting	Sulphide ores (e.g., ZnS)	Heating strongly in excess air	2ZnS + 3O₂ → 2ZnO + 2SO₂
Calcination	Carbonate ores (e.g., ZnCO₃)	Heating strongly in limited air	ZnCO₃ → ZnO + CO₂

(Reference: Science, Class X (NCERT 2025 ed.), Chapter 3, p.51)

Once we have the metal oxide, the method of reduction depends entirely on the metal's position in the reactivity series. For moderately reactive metals like Zinc or Iron, we use reducing agents like Carbon (coke). Carbon acts as a "thief" that steals the oxygen from the metal oxide to form CO₂. However, for highly reactive metals like Sodium or Aluminium, Carbon is useless because these metals have a much higher affinity for oxygen than carbon does. In such cases, we use electrolytic reduction, where electricity is used to force the metal ions to gain electrons at the cathode Science, Class X (NCERT 2025 ed.), Chapter 3, p.52.

Sources: Science, Class X (NCERT 2025 ed.), Chapter 3: Metals and Non-metals, p.51-52

6. The Redox Principle: Classical vs. Modern Definitions (exam-level)

At its core, the Redox Principle (a portmanteau of Reduction and Oxidation) describes the chemical "tug-of-war" for stability. While these terms might sound technical, they govern everything from the energy in your food to the rusting of a bridge. Understanding Redox requires looking through two lenses: the Classical view, which focuses on oxygen and hydrogen, and the Modern view, which focuses on the movement of electrons.

In the Classical Definition, oxidation was originally linked to the addition of oxygen to a substance—such as iron reacting with air to form rust. However, the definition expanded to include the removal of hydrogen or the removal of an electropositive element. Conversely, Reduction is defined as the removal of oxygen, the addition of hydrogen, or the addition of an electropositive element Science, class X (NCERT 2025 ed.), Chapter 1, p.13. For instance, in the reaction CuO + H₂ → Cu + H₂O, copper(II) oxide loses oxygen (reduction) while hydrogen gains oxygen (oxidation) Science, class X (NCERT 2025 ed.), Chapter 1, p.12.

The Modern Electronic Concept provides a more universal explanation: Oxidation is the loss of electrons, and Reduction is the gain of electrons. When an atom loses electrons, its oxidation state increases. This is why obtaining pure metals from their oxides is fundamentally a reduction process—we are forcing the metal ions to gain electrons to return to their elemental state Science, class X (NCERT 2025 ed.), Chapter 3, p.51. Interestingly, this chemical principle even shapes our landscape. In geography, oxidation of iron minerals in the presence of water and air gives soil its distinct red color, while reduction in waterlogged, oxygen-poor environments turns soil greenish or grey Physical Geography by PMF IAS, Geomorphic Movements, p.91.

Process	Classical Definition (Oxygen/Hydrogen)	Modern Definition (Electrons)
Oxidation	Gain of Oxygen OR Loss of Hydrogen	Loss of Electrons
Reduction	Loss of Oxygen OR Gain of Hydrogen	Gain of Electrons

Sources: Science, class X (NCERT 2025 ed.), Chapter 1: Chemical Reactions and Equations, p.12-13; Science, class X (NCERT 2025 ed.), Chapter 3: Metals and Non-metals, p.51; Physical Geography by PMF IAS, Geomorphic Movements, p.91

7. Solving the Original PYQ (exam-level)

Now that you have mastered the foundational definitions of redox reactions, this question serves as a perfect application of the classical concept of oxidation. In your learning path, we established that oxidation is not merely the addition of oxygen, but a broader process involving the movement of hydrogen and other elements based on their electrical character. When you approach this question, you must synthesize the two perspectives: the removal of hydrogen and the behavior of electropositive elements. As noted in NCERT Class X Science (2025 ed.), Chapter 1, these two processes are the inverse of one another in the context of oxidation and reduction.

To arrive at the correct answer, let's walk through the logic: Statement 1 identifies that hydrogen is displaced (removed) from a substance. According to the classical definition, the loss of hydrogen is a definitive indicator of oxidation, making this statement correct. However, Statement 2 suggests that adding an electropositive element constitutes oxidation. This is where the UPSC sets a trap. In chemistry, electropositive elements (like metals) behave similarly to hydrogen; therefore, their addition actually results in reduction. For a process to be oxidation, an electropositive element would need to be removed or an electronegative element added. Thus, Statement 2 is incorrect.

The correct answer is (A) 1 only. The common pitfall here is the confusion between "addition" and "displacement." UPSC often tests your ability to distinguish between these opposites. While Statement 1 correctly identifies a loss (displacement) as oxidation, Statement 2 incorrectly identifies an addition as oxidation. By keeping the Electronic Concept in mind—where oxidation is the loss of electrons—you can verify that adding an electropositive element (which brings electrons with it) must be the opposite of oxidation. Always look for that reciprocal relationship to avoid being caught by these conceptual swaps.