Natural gas is a mixture of gases and contains mainly

1. Introduction to Hydrocarbons: Alkanes (basic)

In the vast world of chemistry, hydrocarbons represent the simplest yet most fundamental class of organic compounds, consisting entirely of carbon and hydrogen. Within this family, we distinguish between "saturated" and "unsaturated" compounds. Alkanes are the saturated hydrocarbons, meaning every carbon atom is linked to others by single covalent bonds, effectively "saturating" the carbon's bonding capacity with hydrogen atoms Science, Carbon and its Compounds, p.65.

Alkanes follow a predictable pattern known as a homologous series, where each member differs from the next by a single -CH₂- unit. They share a general chemical formula of CₙH₂ₙ₊₂. For example, if a molecule has 1 carbon atom (n=1), it is Methane (CH₄); if it has 2, it is Ethane (C₂H₆). As the chain grows, we encounter Propane (C₃H₈) and Butane (C₄H₁₀) Science, Carbon and its Compounds, p.64. Because of their single-bond structure, alkanes are generally stable and unreactive under normal conditions, though they can undergo substitution reactions—where a hydrogen atom is replaced by another atom, like chlorine—in the presence of sunlight Science, Carbon and its Compounds, p.71.

In our everyday lives, the most common source of these alkanes is natural gas. While many think of natural gas as just one substance, it is actually a mixture. Its primary constituent is Methane (often making up over 80-90% of the volume), but it also contains significant amounts of "higher hydrocarbons" or heavier alkanes like ethane, propane, and butane. These additional components are frequently processed into Natural Gas Liquids (NGLs), which are vital for heating and industrial applications.

Alkane Name	Carbon Atoms	Chemical Formula
Methane	1	CH₄
Ethane	2	C₂H₆
Propane	3	C₃H₈
Butane	4	C₄H₁₀

Sources: Science, Carbon and its Compounds, p.64; Science, Carbon and its Compounds, p.65; Science, Carbon and its Compounds, p.71

2. Fossil Fuels: Formation and Classification (basic)

To understand fossil fuels, we must first look at their organic origin. These fuels are essentially ancient solar energy captured by living organisms millions of years ago. When microscopic marine life (fauna), plants (flora), and other vegetal matter died, they were buried under thick layers of silt, mud, and sand in sedimentary basins. Over geological timescales—particularly during the Tertiary Period—these layers were subjected to immense heat and pressure, which triggered complex chemical changes, transforming the organic debris into energy-rich hydrocarbons Environment and Ecology, Majid Hussain, p.14.

Natural Gas is a specific type of fossil fuel that often occurs alongside petroleum. Because gas is lighter than both water and crude oil, it typically accumulates in the anticlines (arch-like folds in rock layers) above the oil deposits Geography of India, Majid Husain, p.9. Chemically, natural gas is not a single substance but a mixture of gaseous hydrocarbons. Its dominant component is Methane (CH₄), which usually makes up 80% to 99% of the total volume. The remainder consists of "higher hydrocarbons" or heavier alkanes such as ethane (C₂H₆), propane (C₃H₈), and butane (C₄H₁₀) Science class X, NCERT 2025 ed., Chapter 4, p.64.

In the broader classification of energy, coal, petroleum, and natural gas are categorized as conventional and exhaustible resources. This means they are finite; once we extract and burn them for power, transport, or industrial processes, they cannot be replaced within a human timeframe INDIA PEOPLE AND ECONOMY, NCERT, p.57.

Fuel Type	Primary State	Main Characteristic
Coal	Solid	Carbon-rich sedimentary rock
Petroleum	Liquid	Complex mixture of liquid hydrocarbons
Natural Gas	Gas	Primarily Methane (CH₄)

Sources: Environment and Ecology, Majid Hussain, Distribution of World Natural Resources, p.14; Geography of India, Majid Husain, Energy Resources, p.9; Science class X, NCERT 2025 ed., Chapter 4: Carbon and its Compounds, p.64; INDIA PEOPLE AND ECONOMY, NCERT, Mineral and Energy Resources, p.57

3. Petroleum Refining and Fractional Distillation (intermediate)

Crude petroleum, often called 'Black Gold,' is a complex cocktail of various hydrocarbons—molecules made of carbon and hydrogen. In its raw, thick, and dark state, it has very little direct utility. To make it useful for our cars, stoves, and industries, we must separate this mixture into its individual components. This is achieved through a process called fractional distillation, which relies on a fundamental physical principle: different substances have different boiling points.

At the molecular level, boiling occurs when the heat energy becomes strong enough to overcome the interparticle forces of attraction, allowing particles to move apart and escape into a gaseous state Science, Class VIII NCERT, Particulate Nature of Matter, p.105. In petroleum, the boiling point is closely tied to the size of the hydrocarbon chain; generally, the more carbon atoms a molecule has, the higher its boiling point Science, Class X NCERT, Carbon and its Compounds, p.59. During refining, crude oil is heated to very high temperatures and pumped into a tall fractionating tower. This tower is hottest at the bottom and gradually cooler toward the top. As the vapours rise, they cool down and condense back into liquids at different heights—or 'fractions'—depending on their specific boiling points Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.269.

Fraction	Chain Length	Boiling Point	Common Use
Refinery Gas	Short (C₁-C₄)	Lowest	Fuel for heating/cooking
Petrol (Gasoline)	Medium (C₅-C₁₀)	Low	Fuel for automobiles
Diesel Oil	Long (C₁₅-C₂₅)	High	Fuel for heavy vehicles
Bitumen	Very Long (C₃₅+)	Highest	Road surfacing

Interestingly, natural distillation often produces more heavy oils (like fuel oil) and less light oil (like petrol) than the market demands. To fix this imbalance, engineers use a process called thermal cracking. By applying extreme heat and pressure, they literally 'crack' or break down the long, heavy hydrocarbon chains into the shorter, more valuable molecules used in petrol Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.271. This industrial capability is why India, despite declining domestic crude production, maintains a massive refining infrastructure to process imported crude oil for both domestic use and export Indian Economy, Nitin Singhania, Infrastructure, p.446.

Sources: Science, Class VIII NCERT, Particulate Nature of Matter, p.105; Science, Class X NCERT, Carbon and its Compounds, p.59; Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.269; Certificate Physical and Human Geography, GC Leong, Fuel and Power, p.271; Indian Economy, Nitin Singhania, Infrastructure, p.446

4. LPG vs. CNG: Domestic and Industrial Fuels (intermediate)

To understand our modern energy landscape, we must distinguish between the two primary gaseous fuels we use daily: LPG and CNG. While both are hydrocarbons, they differ significantly in their chemical 'makeup' and physical properties. Natural Gas, the parent of CNG, is a fossil fuel found in the earth, often alongside petroleum deposits Contemporary India II, p.115. Its primary constituent is Methane (CH₄), which typically accounts for 80% to 90% of its volume. Beyond methane, it contains 'higher hydrocarbons' such as Ethane (C₂H₆), Propane (C₃H₈), and Butane (C₄H₁₀) Science Class X, Carbon and its Compounds, p.64.

LPG (Liquefied Petroleum Gas), on the other hand, is a byproduct of petroleum refining. Unlike natural gas which is mostly methane (1 carbon atom), LPG is a mixture of heavier gases, primarily Propane and Butane (3 and 4 carbon atoms respectively). These gases are liquefied under moderate pressure for easy storage in the familiar red cylinders used in Indian kitchens. In the industrial and transport sectors, natural gas is used in two forms: CNG (Compressed Natural Gas) for vehicles and PNG (Piped Natural Gas) for direct supply to homes and factories Contemporary India II, p.115.

Comparing their characteristics helps us understand why they are used differently in domestic and industrial settings:

Feature	CNG (Natural Gas)	LPG (Petroleum Gas)
Main Component	Methane (CH₄)	Propane (C₃H₈) & Butane (C₄H₁₀)
Weight vs. Air	Lighter than air (disperses quickly)	Heavier than air (settles on the floor)
Source	Gas wells / Petroleum deposits	Crude oil refining process
State	Compressed Gas	Liquefied under pressure

In India, the distribution and competitive marketing of these gases are regulated by the Petroleum and Natural Gas Regulatory Board (PNGRB). If disputes arise regarding PNGRB decisions, the appeals are heard by the Appellate Tribunal for Electricity (APTEL), ensuring a structured legal framework for this vital energy sector Indian Polity, Laxmikanth, p.757.

Sources: Contemporary India II, Mineral and Energy Resources, p.115; Science Class X, Carbon and its Compounds, p.64; Indian Polity, Laxmikanth, World Constitutions (Appendix/Regulatory Bodies), p.757

5. Manufactured Gaseous Fuels (intermediate)

While natural gas is a fossil fuel found deep within the earth—primarily composed of Methane (CH₄) along with heavier hydrocarbons like ethane, propane, and butane—humanity has developed several ways to 'manufacture' gaseous fuels from solid or liquid precursors. These manufactured gases were the backbone of the industrial revolution and remain vital for specific industrial heating and chemical synthesis today. Understanding the difference between a naturally occurring hydrocarbon mixture and a manufactured chemical mixture is a core concept in applied chemistry.

The two most historically significant manufactured gases are Water Gas and Producer Gas. Water gas is created by passing steam over red-hot coke, resulting in a mixture of Carbon Monoxide (CO) and Hydrogen (H₂). Because both components are flammable, it has a high heating value. In contrast, Producer gas is made by passing air over hot coal, which yields a mixture of CO and Nitrogen (N₂). Since nitrogen is inert and does not burn, producer gas has a lower calorific value than water gas. These differ significantly from Natural Gas, which typically contains 80% to 99% methane Environment and Ecology (Majid Hussain), Distribution of World Natural Resources, p.15 and is often found alongside crude oil deposits.

In modern sustainable chemistry, we also look at Biogas. Biogas is a manufactured gas produced through the anaerobic decomposition of organic waste. Like natural gas, its major component is methane, making it an excellent fuel for heating and electricity generation Carbon and its Compounds, Science Class X, p.60. Whether derived from coal (Coal Gas) or biomass, these manufactured fuels provide a flexible way to convert bulky solid energy into a clean-burning, easily transportable gaseous form.

Fuel Type	Primary Components	Origin
Natural Gas	CH₄ + Higher Hydrocarbons	Geological (Fossil)
Water Gas	CO + H₂	Industrial (Steam + Coke)
Producer Gas	CO + N₂	Industrial (Air + Coke)
Biogas	CH₄ + CO₂	Biological Decomposition

Sources: Environment and Ecology (Majid Hussain), Distribution of World Natural Resources, p.15; Science Class X (NCERT 2025 ed.), Carbon and its Compounds, p.60

6. Environmental Impact: Methane as a Greenhouse Gas (exam-level)

When we talk about Natural Gas, we are primarily talking about Methane (CH₄), which makes up about 80% to 99% of its composition Science, class X (NCERT 2025 ed.), Chapter 4, p. 64. While it is a clean-burning fuel in terms of particulate matter, its escape into the atmosphere—whether through leaks or agricultural processes—presents a significant environmental challenge. Methane is a potent Greenhouse Gas (GHG), meaning it excels at trapping infrared radiation (heat) that would otherwise escape into space.

To understand its impact, we use a metric called Global Warming Potential (GWP). GWP measures how much energy the emissions of 1 ton of a gas will absorb over a given period (usually 100 years) relative to 1 ton of Carbon Dioxide (CO₂). Even though methane has a much shorter atmospheric lifetime (about 12 years) compared to CO₂ (which can last centuries), it is far more efficient at trapping heat while it is there Environment, Shankar IAS Academy (ed 10th), Climate Change, p. 260. This is why it is often called a "short-lived climate pollutant."

Feature	Carbon Dioxide (CO₂)	Methane (CH₄)
Atmospheric Lifetime	Variable (centuries)	~12 Years
GWP (100-year)	1 (The baseline)	~21 to 28
Primary Source	Fossil fuel combustion	Anaerobic decay, Livestock, Rice fields

Methane is largely generated through anaerobic processes—biological activity occurring in the absence of oxygen. Approximately 50% of human-linked methane emissions come from enteric fermentation (digestion in livestock like cows) and rice cultivation (underwater bacteria in flooded paddies) Environment and Ecology, Majid Hussain (3rd ed.), Climate Change, p. 11. Because of its high warming potential, international agreements like the Kyoto Protocol and the recent Global Methane Pledge (aiming for a 30% reduction by 2030) specifically target methane to slow down immediate global temperature rises Contemporary World Politics, NCERT Class XII, Environment and Natural Resources, p. 87.

Sources: Science, class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.64; Environment, Shankar IAS Academy (ed 10th), Climate Change, p.260; Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Climate Change, p.11; Contemporary World Politics, Textbook in political science for Class XII (NCERT 2025 ed.), Environment and Natural Resources, p.87

7. Deep Dive: Composition of Natural Gas (exam-level)

Natural gas is a naturally occurring fossil fuel that exists as a complex mixture of gaseous hydrocarbons. It is often found trapped in the Earth's crust, either alone or in association with crude oil deposits. The defining characteristic of natural gas is its overwhelmingly high concentration of Methane (CH₄), which typically accounts for 80% to 99% of its total composition Environment and Ecology, Majid Hussain, Distribution of World Natural Resources, p.15. Because methane is the simplest hydrocarbon, natural gas burns relatively cleanly compared to other fossil fuels, releasing fewer pollutants and residues.

While methane is the primary constituent, "raw" natural gas is rarely pure. It contains varying amounts of higher hydrocarbons (heavier alkanes), which include:

• Ethane (C₂H₆)
• Propane (C₃H₈)
• Butane (C₄H₁₀)
• Pentane (C₅H₁₂)

In industrial processing, these heavier components are often extracted and categorized as Natural Gas Liquids (NGLs). It is vital for UPSC aspirants to distinguish natural gas from manufactured gases. For instance, while natural gas is hydrocarbon-based, gases like "water gas" or "producer gas" are primarily composed of Carbon Monoxide (CO) and Hydrogen (H₂). Natural gas may contain trace non-hydrocarbon impurities like Nitrogen (N₂), Carbon Dioxide (CO₂), and Hydrogen Sulfide (H₂S), but these are minor components compared to the hydrocarbon bulk.

In the Indian context, natural gas has become a cornerstone of the energy sector, particularly in the production of chemical fertilizers (which consumes about 40% of the supply) and power generation Geography of India, Majid Husain, Energy Resources, p.17. With the growth of infrastructure, it is now widely used as CNG (Compressed Natural Gas) for transport and PNG (Piped Natural Gas) for households. India's most significant reserves are located in Mumbai High, the Cambay basin, and the Krishna-Godavari (KG) basin India People and Economy, NCERT Class XII, Mineral and Energy Resources, p.61.

Component Type	Specific Gases	Typical Percentage
Primary Hydrocarbon	Methane (CH₄)	80% – 99%
Higher Hydrocarbons (NGLs)	Ethane, Propane, Butane	1% – 15%
Trace Impurities	N₂, CO₂, H₂S	Trace amounts

Sources: Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Distribution of World Natural Resources, p.15; Geography of India ,Majid Husain, (McGrawHill 9th ed.), Energy Resources, p.17; INDIA PEOPLE AND ECONOMY, TEXTBOOK IN GEOGRAPHY FOR CLASS XII (NCERT 2025 ed.), Mineral and Energy Resources, p.61; FUNDAMENTALS OF HUMAN GEOGRAPHY, CLASS XII (NCERT 2025 ed.), Transport and Communication, p.66

8. Solving the Original PYQ (exam-level)

Now that you have mastered the structural chemistry of alkanes and the versatility of carbon chains, this question allows you to apply those building blocks to a real-world energy source. In your learning path, you discovered that carbon forms homologous series where each successive member adds a -CH₂- unit. In nature, Natural Gas exists as a mixture of these varied chain lengths. While methane (CH₄) is the simplest and most abundant component—often making up over 80% of the volume—it is almost always found in geological reservoirs alongside its "chemical siblings," such as ethane, propane, and butane. These are the higher hydrocarbons mentioned in the correct answer, (A) methane and higher hydrocarbons, which are often separated during processing as Natural Gas Liquids (NGLs).

To arrive at the correct answer, you must navigate the specific traps UPSC often sets for students. A common pitfall is choosing option (C), "methane only"; however, in competitive exams, absolute terms like "only" are frequently incorrect because they ignore the trace impurities and associated gases found in raw fossil fuels. Option (B) mentions butane and isobutene, which is a distractor designed to confuse Natural Gas with LPG (Liquefied Petroleum Gas). Meanwhile, option (D) includes hydrogen and carbon monoxide—gases that are characteristic of manufactured industrial fuels like water gas, rather than naturally occurring fossil deposits. As noted in Science, Class X (NCERT 2025 ed.), understanding these chains, branches, and rings is key to identifying the composition of the fuels that power our world.