Which is the primary component of natural gas ?

1. Introduction to Hydrocarbons: Alkanes (basic)

Welcome to our journey into the chemistry of everyday life! To understand the fuels that power our stoves and vehicles, we must first meet the simplest family of organic compounds: Hydrocarbons. As the name suggests, these are substances made entirely of just two elements: Carbon and Hydrogen. Among these, the most fundamental group is the Alkanes.

Alkanes are known as saturated hydrocarbons. In chemistry, "saturated" means that every carbon atom in the molecule is connected to other atoms by single bonds only. Because carbon has a valency of four, it tries to bond with as many hydrogen atoms as possible. This makes alkanes very stable and relatively unreactive under normal conditions, which is why they are sometimes called "paraffins" (from the Latin parum affinis, meaning "little affinity"). However, they can undergo a substitution reaction—for example, when chlorine replaces a hydrogen atom in the presence of sunlight Science, Class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.71.

The names of Alkanes follow a specific pattern based on the number of carbon atoms they contain. They all follow the general chemical formula CₙH₂ₙ₊₂. This means if you know the number of carbons (n), you can always calculate the hydrogens! Let's look at the first few members of this series Science, Class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.64:

No. of C atoms	Name	Formula	Common Use
1	Methane	CH₄	Primary component of Natural Gas & Biogas
2	Ethane	C₂H₆	Chemical feedstock
3	Propane	C₃H₈	LPG (Cooking gas)
4	Butane	C₄H₁₀	Lighter fluid & LPG component

Sources: Science, Class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.64; Science, Class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.65; Science, Class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.71

2. Origin and Formation of Fossil Fuels (basic)

To understand fossil fuels, we must start with the word 'fossil'. Just as a dinosaur bone is a fossilized remains of an animal, coal, petroleum, and natural gas are the 'fossilized' remains of ancient biomass. These fuels are essentially concentrated solar energy stored millions of years ago by plants and microorganisms through photosynthesis. When these organisms died, they didn't just decay into the soil; instead, they were buried under layers of silt, sand, and clay in specific environments like shallow marine basins, deltas, or dense swampy forests Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Chapter 9, p.14.

The transformation from 'dead matter' to 'fuel' requires a very specific recipe of Heat, Pressure, and Time. As more layers of sediment accumulated over the organic matter, the weight created immense pressure. Combined with the internal heat of the Earth and the total absence of oxygen (anaerobic conditions), the organic molecules underwent a slow chemical breakdown. For instance, while terrestrial vegetation in swamps eventually formed coal, microscopic marine organisms (plankton) and algae buried in ocean floors transformed into petroleum and natural gas Geography of India, Majid Husain (McGrawHill 9th ed.), Energy Resources, p.9.

Once formed, these fuels don't always stay where they were born. Because oil and gas are lighter than water, they migrate upward through porous rocks (like sandstone) until they hit an impermeable 'cap rock' that traps them. Geologically, these are often found in sedimentary basins, where the oil is held in the tiny pores of the rock, much like water is held in a sponge Science, class X (NCERT 2025 ed.), Chapter 4, p.70. Depending on the intensity of the heat and the type of organic starting material, we get different end products:

Fuel Type	Primary Origin	Formation Environment
Coal	Land-based plants/trees	Swamps and coastal wetlands
Petroleum	Marine microorganisms/Algae	Shallow marine sediments
Natural Gas	Both (often formed with oil)	High-heat environments

Sources: Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Distribution of World Natural Resources, p.14; Geography of India, Majid Husain (McGrawHill 9th ed.), Energy Resources, p.9; Science, class X (NCERT 2025 ed.), Carbon and its Compounds, p.70

3. Petroleum Refining and Fractional Distillation (basic)

When we extract Crude Oil (petroleum) from the Earth, it is a thick, dark liquid that is practically useless in its raw form. Think of it as a complex 'cocktail' of various substances called hydrocarbons—compounds made entirely of hydrogen and carbon. To make this mixture useful for our cars, planes, and industry, we must separate these hydrocarbons into specific groups or 'fractions.' This process is known as Petroleum Refining, and its heart is a technique called Fractional Distillation.

The core scientific principle here is the Boiling Point. Every substance has a specific temperature at which its particles gain enough energy to break free from liquid bonds and turn into vapor Science, Class VIII NCERT, Particulate Nature of Matter, p.105. In a refinery, crude oil is heated to very high temperatures (around 400°C) and pumped into a tall fractionating column. Because different hydrocarbons have different boiling points, they 'boil off' and condense back into liquids at different heights within the tower Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.269. Carbon compounds like Methane have very low boiling points (111 K) and remain gases even at low temperatures, while heavier compounds remain liquid or solid until much higher temperatures Science, Class X NCERT, Carbon and its Compounds, p.59.

As the hot vapors rise through the tower, they cool down. The 'heavy' fractions with high boiling points condense into liquids near the bottom, while 'lighter' fractions rise higher before cooling enough to condense. This allows us to tap off different products at various levels:

Fraction	Boiling Point Range	Common Use
Refinery Gas	Lowest	Fuel for heating, LPG
Petrol (Gasoline)	Low	Fuel for light vehicles
Kerosene	Medium	Jet fuel, domestic heating
Diesel	High	Fuel for trucks and buses
Bitumen	Highest	Road surfacing and roofing

Interestingly, our modern world demands much more petrol than a simple distillation tower naturally provides. To solve this, refineries use a process called Thermal Cracking. In this stage, heavier, less-demanded fractions are heated to extreme temperatures until their large molecules literally 'crack' or break down into the lighter, more valuable molecules found in petrol Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.271.

Sources: Science, Class VIII NCERT, Particulate Nature of Matter, p.105; Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.269; Science, Class X NCERT, Carbon and its Compounds, p.59; Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.271

4. Biogas and Anaerobic Digestion (intermediate)

Biogas is a renewable energy source produced through the biological breakdown of organic matter—such as cattle dung, agricultural waste, and municipal waste—in the absence of oxygen. This chemical process is known as anaerobic digestion. In rural India, these systems are popularly called 'Gobar gas plants' because they primarily utilize cattle dung as feedstock NCERT, Contemporary India II: Geography Class X, Ch. 5: Minerals and Energy Resources, p.117. Beyond just waste management, the process yields a clean-burning fuel and a nutrient-rich slurry that serves as an excellent organic fertilizer.

The primary constituent of biogas is Methane (CH₄), which typically makes up about 50–75% of the gas, followed by Carbon Dioxide (CO₂) and trace amounts of other gases like Hydrogen Sulfide. Biogas is highly valued because it has a higher thermal efficiency compared to traditional fuels like kerosene, dung cakes, or charcoal NCERT, Contemporary India II: Geography Class X, Ch. 5: Minerals and Energy Resources, p.117. While it is an excellent fuel, we must manage it carefully; CH₄ is a potent greenhouse gas with a Global Warming Potential (GWP) more than 20 times higher than that of CO₂ over a 100-year period Shankar IAS Academy, Environment 10th Ed., Ch. Climate Change, p.260.

Feature	Biogas (Anaerobic Digestion)	Traditional Bio-fuels (Dung Cakes/Wood)
Thermal Efficiency	High	Low
Pollution	Clean burning, smokeless	High indoor air pollution (smoke)
By-products	Enriched manure (slurry)	Ash (low nutrient value)

Recognizing its potential for energy security, the Government of India has long supported this technology. The National Biogas and Manure Management Programme (NBMMP), implemented by the Ministry of New and Renewable Energy (MNRE), has overseen the installation of over 50 lakh family-type biogas plants across the country Nitin Singhania, Indian Economy 2nd Ed., Ch. Infrastructure, p.453. This initiative not only provides clean energy for cooking and lighting but also empowers rural households by reducing their dependence on expensive fossil fuels.

Sources: NCERT, Contemporary India II: Geography Class X, Print Culture and the Modern World (Note: Excerpt refers to Energy resources), p.117; Shankar IAS Academy, Environment 10th Ed., Climate Change, p.260; Nitin Singhania, Indian Economy 2nd Ed., Infrastructure, p.453; NCERT, Science Class VIII (2025 Ed.), The Invisible Living World: Beyond Our Naked Eye, p.27

5. Environmental Impact: Methane as a Greenhouse Gas (intermediate)

Methane (CH₄) is the simplest hydrocarbon, consisting of one carbon atom covalently bonded to four hydrogen atoms Science, class X (NCERT 2025 ed.), Chapter 4, p.60. While it is the primary component of natural gas (making up 80% to 90% of its volume), Compressed Natural Gas (CNG), and biogas, it is also one of the most significant contributors to the greenhouse effect Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Chapter 9, p.15. Since the Industrial Revolution, atmospheric concentrations of methane have more than doubled, currently increasing at a rate of approximately 1% per year Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Climate Change, p.11.

To understand methane's impact, we use a metric called Global Warming Potential (GWP). This measures how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO₂). While CO₂ serves as the baseline (GWP of 1), methane is a much more potent "heat-trapper." On a 100-year timescale, methane has a GWP more than 20 times higher than CO₂ Environment, Shankar IAS Academy (ed 10th), Climate Change, p.260. This means that although there is less methane in the atmosphere than CO₂, each molecule of methane is far more effective at absorbing infrared radiation and warming the planet.

However, methane differs from CO₂ in its atmospheric residence time. While CO₂ can linger for centuries, methane is relatively short-lived, lasting an average of only 12 years before it breaks down Environment, Shankar IAS Academy (ed 10th), Climate Change, p.260. This short lifespan combined with high potency makes methane a critical target for climate action; reducing methane emissions can lead to a relatively rapid slowdown in the rate of global warming. This logic underpins international efforts like the Global Methane Pledge, which aims to cut global methane emissions by 30% by the year 2030 Environment, Shankar IAS Academy (ed 10th), Climate Change Organizations, p.335.

Feature	Carbon Dioxide (CO₂)	Methane (CH₄)
Atmospheric Lifetime	Hundreds of years	Approximately 12 years
Global Warming Potential (100-yr)	1 (Baseline)	20+ times higher than CO₂
Primary Source	Fossil fuel combustion	Agriculture, landfills, natural gas leaks

Sources: Science, class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.60; Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Chapter 9: Distribution of World Natural Resources, p.15; Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Climate Change, p.11; Environment, Shankar IAS Academy (ed 10th), Climate Change, p.260; Environment, Shankar IAS Academy (ed 10th), Climate Change Organizations, p.335

6. Gaseous Fuels Comparison: LPG vs. CNG (exam-level)

When we talk about gaseous fuels in our homes or vehicles, we are essentially discussing hydrocarbons—compounds made of carbon and hydrogen. To understand the difference between LPG (Liquefied Petroleum Gas) and CNG (Compressed Natural Gas), we must look at their chemical "DNA." As we see in the homologous series of alkanes, hydrocarbons range from the very simple Methane (CH₄), which has just one carbon atom, to Butane (C₄H₁₀), which has four Science, Class X (NCERT 2025 ed.), Chapter 4, p.64. The number of carbon atoms determines how these gases behave under pressure and how they burn.

CNG is primarily Methane (CH₄). It is sourced from natural gas deposits often found alongside petroleum Contemporary India II, Class X (NCERT 2022 ed.), Chapter 5, p.52. Because methane is a very light molecule, it does not turn into a liquid easily at room temperature; therefore, we "compress" it at very high pressure to store it in cylinders. On the other hand, LPG is a mixture of Propane (C₃H₈) and Butane (C₄H₁₀). These are heavier molecules that can be turned into a liquid under relatively low pressure, which is why your kitchen cylinder contains liquid that turns back into gas when the valve is opened.

From a safety and environmental perspective, the differences are vital for a civil servant to understand. CNG is lighter than air, meaning if there is a leak, it rises and disperses quickly. LPG is heavier than air; it tends to settle near the ground or in drains, posing a higher risk of fire in case of a leak. Furthermore, CNG is considered "greener" because methane produces the least amount of CO₂ per unit of energy compared to more complex hydrocarbons.

Feature	CNG (Compressed Natural Gas)	LPG (Liquefied Petroleum Gas)
Primary Component	Methane (CH₄)	Propane (C₃H₈) & Butane (C₄H₁₀)
Density	Lighter than air (rises)	Heavier than air (settles)
Physical State in Tank	High-pressure gas	Liquefied under moderate pressure
Source	Natural gas wells / Petroleum deposits	By-product of petroleum refining

Sources: Science, Class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.64; Contemporary India II, Class X (NCERT 2022 ed.), Chapter 5: Minerals and Energy Resources, p.52

7. Chemical Profile of Natural Gas (intermediate)

At its heart, Natural Gas is not a single chemical substance but a mixture of gaseous hydrocarbons formed deep underground from the remains of ancient marine organisms. The 'superstar' of this mixture is Methane (CH₄), the simplest hydrocarbon, consisting of one carbon atom covalently bonded to four hydrogen atoms. In most natural gas deposits, methane accounts for a staggering 80% to 90% of the total volume, making it the primary constituent that dictates the fuel's properties Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Chapter 9, p. 15. Because of this high methane content, natural gas is the cleanest burning fossil fuel, producing fewer pollutants like sulfur dioxide or nitrogen oxides compared to coal or oil. While methane dominates, natural gas is a 'cocktail' that includes other heavier hydrocarbons. These include Ethane (C₂H₆), Propane (C₃H₈), and Butane (C₄H₁₀). During industrial processing, these heavier gases are often stripped out to ensure the gas reaching your home or factory is of consistent quality. Interestingly, this chemical profile remains consistent across different forms of 'green' or 'compressed' energy; for instance, methane is also the major component of Biogas and Compressed Natural Gas (CNG) Science, class X (NCERT 2025 ed.), Chapter 4, p. 60. Beyond just being a fuel, the chemical profile of natural gas makes it a vital industrial feedstock. In India, its largest share (about 40%) is consumed in the production of chemical fertilizers, while approximately 30% goes toward power generation Geography of India, Majid Husain, (McGrawHill 9th ed.), Energy Resources, p. 17. It is important to note that while it is a 'cleaner' fuel, methane itself is a potent greenhouse gas if leaked directly into the atmosphere, possessing a much higher heat-trapping capability than carbon dioxide over a short timeframe.

Typical Composition of Natural Gas:

Component	Chemical Formula	Approx. Percentage
Methane	CH₄	80% – 95%
Ethane	C₂H₆	2% – 5%
Propane/Butane	C₃H₈ / C₄H₁₀	Traces/Variable
Other (CO₂, N₂, He)	-	Small amounts

Sources: Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Chapter 9: Distribution of World Natural Resources, p.15; Science, class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.60; Geography of India, Majid Husain, (McGrawHill 9th ed.), Energy Resources, p.17

8. Solving the Original PYQ (exam-level)

Now that you have mastered the fundamental chemistry of hydrocarbons and the formation of fossil fuels, this question allows you to apply those building blocks to a real-world scenario. You have learned that hydrocarbons are categorized by the length of their carbon chains; the core concept here is that the most volatile and abundant of these in the Earth's crust is the simplest one-carbon molecule. According to Science, class X (NCERT 2025 ed.), the covalent bonding in Methane makes it a highly stable and energetic fuel, which is why it serves as the foundational unit for most gaseous energy sources we extract.

To arrive at the correct answer, (A) Methane, you must focus on the qualifier "primary." While natural gas is technically a mixture, methane typically accounts for a staggering 80% to 90% of its total volume. Your reasoning should follow the logic of processing: as natural gas is refined, heavier molecules are often removed to maintain quality. As noted in Environment and Ecology, Majid Hussain, this dominance is why methane is the chief constituent not just in natural gas, but also in Compressed Natural Gas (CNG) and bio-gas. If the question asks for the "major" or "primary" component of any of these, methane is almost always your target.

UPSC often uses Butane and Propane as distractor options to test your ability to distinguish between different fuel types. These two gases are the primary components of LPG (Liquefied Petroleum Gas), which is a common point of confusion for students. Similarly, Ethane is present in natural gas but only in minor quantities. The trap here is the shared chemical family; by remembering that natural gas is the "lightest" fossil fuel mixture dominated by the simplest hydrocarbon, you can avoid these heavier-chain traps and confidently select the right option.