Consider the following statements : 1. Baking soda is used in fire extinguishers. 2. Quick lime is used in the manufacture of glass. Which of the statements given above is/are correct ?

1. Common Sodium Compounds and their Properties (basic)

Welcome to our first step into Applied Everyday Chemistry. To understand how chemistry shapes our world, we must start with one of the most versatile elements on the periodic table: Sodium. In nature, sodium is highly reactive, so we mostly encounter it as part of stable compounds known as salts. A salt is typically formed through a neutralisation reaction, where an acid reacts with a base to produce salt and water Science, Class X, p.21. While common salt (Sodium Chloride, NaCl) is the most famous, other sodium compounds like Baking Soda and Washing Soda play critical roles in our homes and industries.

Sodium Hydrogencarbonate (NaHCO₃), commonly known as Baking Soda, is a mild, non-corrosive basic salt Science, Class X, p.31. Its "basic" nature makes it an excellent antacid for neutralising excess stomach acid. However, its most fascinating property is how it reacts to heat. When heated during cooking, it decomposes to release Carbon Dioxide (CO₂) gas. This gas creates bubbles that make cakes and breads rise. This same property—the ability to release CO₂—makes it a vital component in soda-acid fire extinguishers, where the gas helps smother flames by displacing the oxygen they need to burn.

Another heavy-hitter is Sodium Carbonate (Na₂CO₃), or Washing Soda. Both the carbonate and hydrogencarbonate forms of sodium react with acids to produce a salt, water, and carbon dioxide Science, Class X, p.74. In industrial chemistry, Sodium Carbonate (often called soda ash) is indispensable for manufacturing glass. Specifically, it is melted with silica and lime to create soda-lime glass, which makes up the vast majority of our windows and bottles.

Compound	Common Name	Key Property/Use
NaHCO₃	Baking Soda	Releases CO₂ when heated; used as an antacid and in fire extinguishers.
Na₂CO₃	Washing Soda / Soda Ash	Basic salt; essential in glass and soap manufacturing.
NaCl	Common Salt	Neutral salt (pH ~7); raw material for many other chemicals.

Sources: Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.21; Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.31; Science, Class X (NCERT 2025 ed.), Carbon and its Compounds, p.74

2. Calcium Compounds: From Limestone to Quicklime (basic)

To understand the chemistry of construction and daily life, we must look at the fascinating cycle of Calcium compounds. It all starts with Limestone (Calcium Carbonate, CaCO₃). In nature, this is a sedimentary rock formed over millions of years from the accumulation of corals and shells Certificate Physical and Human Geography, Limestone and Chalk Landforms, p.76. Whether it appears as soft chalk or hard marble, the chemical identity remains the same: CaCO₃ Science Class X, Chemical Reactions and Equations, p.7.

The industrial journey begins when we heat limestone in a kiln. This process, known as thermal decomposition, breaks down the limestone into Quicklime (Calcium Oxide, CaO) and releases carbon dioxide gas Science Class X, Chemical Reactions and Equations, p.8. Quicklime is a powerhouse of industrial chemistry; it is a critical raw material in the manufacture of cement and acts as a vital stabilizer in glass production, ensuring the glass is durable and insoluble in water.

Common Name	Chemical Name	Formula	Primary Use
Limestone / Marble	Calcium Carbonate	CaCO₃	Building material, raw source
Quicklime	Calcium Oxide	CaO	Cement and Glass manufacturing
Slaked Lime	Calcium Hydroxide	Ca(OH)₂	Whitewashing, soil treatment

When you add water to quicklime, a vigorous combination reaction occurs, releasing a significant amount of heat—this is why the container feels hot to the touch Science Class VIII, Nature of Matter, p.118. The resulting substance is Slaked Lime (Calcium Hydroxide, Ca(OH)₂). Historically used for whitewashing walls, slaked lime eventually absorbs CO₂ from the atmosphere to turn back into a thin, hard, and shiny layer of calcium carbonate, effectively closing the "Lime Cycle" Science Class X, Chemical Reactions and Equations, p.6-7.

Sources: Science Class X (NCERT 2025 ed.), Chemical Reactions and Equations, p.6-8; Certificate Physical and Human Geography (GC Leong), Limestone and Chalk Landforms, p.76; Science Class VIII (NCERT 2025 ed.), Nature of Matter: Elements, Compounds, and Mixtures, p.118

3. Industrial Chemistry: Cement and Mortar (intermediate)

At its core, Cement is a hydraulic binder—a substance that sets and hardens to bind other materials together. In industrial chemistry, the most common variety is Portland Cement. It is classified as a non-metallic mineral-based industry because its primary raw materials are minerals extracted from the earth Fundamentals of Human Geography, Secondary Activities, p.41. The chemistry of cement involves a precise balance of Limestone (Calcium Carbonate, CaCO₃), which provides lime (CaO), and Clay, which provides Silica (SiO₂), Alumina (Al₂O₃), and Iron Oxide (Fe₂O₃). During manufacturing, these raw materials are heated in a massive rotary kiln at temperatures reaching 1450°C. This process, known as calcination, causes chemical reactions that fuse the materials into small, marble-sized pellets called Clinker. However, ground clinker alone reacts too violently with water, hardening almost instantly. To prevent this "flash setting," a small amount (2-3%) of Gypsum (CaSO₄·2H₂O) is added during the final grinding process. Gypsum acts as a retardant, slowing down the setting time so that workers have enough time to mix, transport, and apply the material Geography of India, Resources, p.28. While cement is the glue, Mortar is the specific application used to bind bricks or stones. It is created by mixing cement with fine aggregate (sand) and water. In contrast, Concrete adds coarse aggregate (gravel or crushed stone) to the mix for structural strength. Because the raw materials like limestone and gypsum are bulky and lose weight during the heating process (due to the loss of CO₂), cement factories are typically located near mineral sources to minimize transport costs Fundamentals of Human Geography, Secondary Activities, p.38. From an environmental perspective, the production of cement is a significant source of pollution. The process releases large amounts of CO₂ and fine dust particles. This dust can settle on leaves, reducing agricultural yields and causing respiratory issues in humans and animals Exploring Society: India and Beyond, Natural Resources and Their Use, p.15. Modern industrial chemistry is now focusing on "Green Cement," which uses industrial by-products like fly ash or slag to reduce the carbon footprint and mineral consumption.

Sources: Fundamentals of Human Geography, Secondary Activities, p.38, 41; Exploring Society: India and Beyond, Natural Resources and Their Use, p.15; Geography of India, Resources, p.28

4. Chemicals in Agriculture: Soil pH Management (intermediate)

In the world of agriculture, soil is not just 'dirt'; it is a living chemical laboratory. One of the most critical factors determining a plant's health is Soil pH, which measures the concentration of hydrogen ions (H⁺) in the soil solution. On the pH scale of 0 to 14, a value of 7 is neutral. While a perfectly neutral soil is often cited as 7.0, in practical field conditions, a pH of around 7.2 is often considered neutral, with anything significantly lower being labeled acidic Geography of India, Soils, p.3. When soil becomes too acidic, essential nutrients like phosphorus become 'locked' and unavailable to the plant, while toxic elements like aluminum can become more soluble, harming root growth.

Why does soil become acidic? While natural weathering and rainfall play a role, modern conventional agriculture often accelerates this process. The excessive use of certain chemical fertilizers—particularly nitrogen-based ones—can increase the H⁺ ion concentration over time, making the soil hostile to most crops Science-Class VII, Exploring Substances, p.18. To restore balance, farmers must perform a 'neutralization' reaction. This is done by adding bases to the soil, a process commonly known as liming. These basic substances react with the acid in the soil to form water and salt, thereby raising the pH back to a range where plants can thrive.

The choice of chemical for soil treatment depends on the severity of the acidity and the desired speed of reaction. Farmers typically use three primary calcium-based compounds:

Chemical Name	Common Name	Formula	Characteristics
Calcium Oxide	Quick lime	CaO	Very strong base; reacts quickly with moisture.
Calcium Hydroxide	Slaked lime	Ca(OH)₂	Effective neutralizer; often used in powder form.
Calcium Carbonate	Chalk or Limestone	CaCO₃	Milder and slower-acting; common for long-term maintenance.

Note: If a soil were instead too alkaline (basic), a farmer might add organic matter or compost, which releases acids during decomposition to bring the pH down Science, Acids, Bases and Salts, p.28.

Sources: Geography of India, Soils, p.3; Science-Class VII, Exploring Substances: Acidic, Basic, and Neutral, p.18; Science, Acids, Bases and Salts, p.28

5. Chemistry of Fire Extinguishers (exam-level)

To understand how fire extinguishers work, we must first look at the Fire Triangle: fuel, heat, and oxygen. A fire persists only as long as all three are present. Chemistry helps us break this triangle, most commonly by cutting off the oxygen supply or cooling the fuel. The most iconic example in everyday chemistry is the Soda-Acid Fire Extinguisher. This device relies on a simple yet powerful chemical reaction between an acid and a metal hydrogencarbonate to produce Carbon Dioxide (CO₂).

In a typical soda-acid setup, a container holds a solution of Sodium Hydrogencarbonate (Baking Soda, NaHCO₃). Inside, a separate small bottle or ignition tube contains dilute Sulphuric Acid (H₂SO₄). When the extinguisher is operated (often by tilting or striking a plunger), the acid mixes with the baking soda solution. As noted in Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p. 36, this reaction is:
2NaHCO₃ + H₂SO₄ → Na₂SO₄ + 2H₂O + 2CO₂.
The rapid evolution of CO₂ gas creates pressure, forcing the liquid and gas out through the nozzle toward the flames.

Why use Carbon Dioxide? CO₂ is denser than air. When sprayed over a fire, it sinks and blankets the burning material, effectively displacing the surrounding oxygen. Because the fire can no longer 'breathe,' it is smothered. Furthermore, sodium hydrogencarbonate is ideal for this role because it is stable, non-toxic, and also decomposes when it hits the heat of the fire to release even more CO₂ Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p. 31. This dual action—chemical reaction inside the canister and thermal decomposition on the fire—makes baking soda a cornerstone of fire safety chemistry.

Sources: Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.31; Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.36

6. Raw Materials and Stabilizers in Glass Manufacturing (exam-level)

To understand glass manufacturing, we must look at it as a delicate chemical balance. At its core, glass is primarily made of Silica (SiO₂), which is the main constituent of sand and Quartz Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.175. However, pure silica has an incredibly high melting point (around 1700°C), making it difficult and expensive to work with industrially. To solve this, we add a flux — typically Sodium Carbonate (Washing Soda, Na₂CO₃) — which lowers the melting point significantly Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.32. While this makes the mixture easier to melt, it creates a new problem: the resulting glass would be soluble in water (known as 'water glass').

This is where Stabilizers come in. To ensure the glass doesn't dissolve and remains chemically durable, Calcium Oxide (Quicklime, CaO) or limestone is added. This 'stabilizes' the mixture, providing the structural integrity and water-insolubility we expect from everyday glassware. The resulting product is known as Soda-Lime Glass, which accounts for nearly 90% of all glass produced today, including windows and bottles. Other materials like Feldspar may also be added to provide aluminium, which further enhances the glass's resistance to chemical corrosion Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.175.

The chemistry of these raw materials often involves the release of gases during the heating process. For instance, when limestone (calcium carbonate) or soda ash is heated in the furnace, they decompose and release Carbon Dioxide (CO₂). Interestingly, this same gas is what turns lime water milky in laboratory experiments, a classic test for identifying the presence of CO₂ Science-Class VII, Changes Around Us, p.60. In the glass furnace, however, this gas escapes, leaving behind the oxides that form the clear, solid glass lattice.

Sources: Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.175; Science, Class X (NCERT 2025 ed.), Acids, Bases and Salts, p.32; Science-Class VII . NCERT(Revised ed 2025), Changes Around Us: Physical and Chemical, p.60

7. Solving the Original PYQ (exam-level)

This question perfectly synthesizes your knowledge of industrial chemistry and the chemical properties of common compounds. You recently explored how Baking Soda (Sodium Hydrogencarbonate) behaves when subjected to heat or acid—specifically its ability to release Carbon Dioxide (CO2). Simultaneously, your study of Calcium compounds highlighted Quick Lime (Calcium Oxide) as a versatile industrial agent. Statement 1 tests your understanding of gas evolution reactions, while Statement 2 evaluates your knowledge of material stabilizers in manufacturing processes, as detailed in Science, Class X (NCERT).

To arrive at the correct answer, (C) Both 1 and 2, let's trace the coach's logic: first, recall that fire extinguishers need a mechanism to displace oxygen; since Baking Soda decomposes to yield CO2, it is a primary ingredient in soda-acid extinguishers. Second, consider the composition of soda-lime glass, the most common glass type. Here, Quick Lime acts as a chemical stabilizer that prevents the glass from being water-soluble, a role distinct from its well-known use in cement. By verifying that both compounds serve these specific industrial functions, you can confidently navigate through the options.

A common trap in UPSC is the "narrow utility" fallacy—where a student might assume Quick Lime is only used for white-washing or cement, thereby incorrectly dismissing Statement 2. Similarly, candidates often confuse Baking Soda with Washing Soda or Bleaching Powder. UPSC frequently tests these overlapping applications of everyday chemicals. Understanding that Quick Lime provides the necessary calcium for durability in glass and that Baking Soda is chosen for its CO2-releasing properties ensures you don't fall for distractors like (A) or (B), even when the uses seem distinct across different industries.