The main constituent of Gobar gas is

1. Classification of Energy Resources (basic)

To understand the chemistry of energy, we must first look at how we categorize its sources. In the simplest terms, energy is the capacity to do work—whether it is the heat required to cook a meal or the electricity needed to power a city NCERT Contemporary India II, Chapter 5, p.113. We typically classify energy resources into two broad categories based on their history of usage and their sustainability: Conventional and Non-conventional sources.

Conventional energy sources are those that have been in use for a long time and are traditionally the mainstays of our energy supply. This includes fossil fuels like coal, petroleum, and natural gas, as well as traditional fuels used in rural households like firewood and cattle dung cakes NCERT Contemporary India II, Chapter 5, p.113. While these sources are widely accessible, most are exhaustible (non-renewable), meaning they take millions of years to form and cannot be replaced once consumed. Furthermore, the combustion of fossil fuels releases gases like CO₂ (Carbon Dioxide), leading to environmental concerns NCERT Contemporary India II, Chapter 5, p.117.

On the other hand, Non-conventional sources (also known as Renewable or Sustainable energy) are alternatives that have gained importance more recently. These include solar, wind, tidal, geothermal, and biogas Geography of India Majid Husain, Chapter 9, p.27. Unlike fossil fuels, these are inexhaustible and generally cleaner. For example, solar and wind energy are fairly non-polluting, although some biological sources like biomass can still contribute to indoor air pollution if not managed correctly Environment Shankar IAS Academy, Chapter 15, p.287.

Feature	Conventional Sources	Non-conventional Sources
Examples	Coal, Petroleum, Firewood, Cattle dung cakes	Solar, Wind, Biogas, Geothermal, Tidal
Availability	Mostly exhaustible (except hydel)	Renewable and sustainable
Environmental Impact	High pollution (GHG emissions)	Generally clean and eco-friendly

Sources: NCERT Contemporary India II, Chapter 5: Minerals and Energy Resources, p.113, 117; Geography of India Majid Husain, Chapter 9, p.27; Environment Shankar IAS Academy, Chapter 15: Renewable Energy, p.287

2. Basics of Hydrocarbons: Alkanes (intermediate)

To master the chemistry of everyday fuels, we must first understand the foundation: **Hydrocarbons**. These are organic compounds consisting entirely of hydrogen and carbon. Within this family, we find **Alkanes**, which are classified as **saturated hydrocarbons**. They are called 'saturated' because the carbon atoms are linked together by only **single covalent bonds**, meaning the carbon atoms are 'filled' to their maximum capacity with hydrogen atoms Science, class X (NCERT 2025 ed.), Chapter 4, p.65. Because of these strong single bonds, alkanes are generally stable and **fairly unreactive** compared to their cousins (alkenes and alkynes).

The simplest alkane is **Methane (CH₄)**, which is the primary constituent of biogas (commonly known as Gobar gas) and Compressed Natural Gas (CNG) Science, class X (NCERT 2025 ed.), Chapter 4, p.60. As the number of carbon atoms increases, we follow a predictable naming pattern and a general formula of CₙH₂ₙ₊₂. You can see the progression in the table below:

No. of Carbon Atoms	Name	Formula
1	Methane	CH₄
2	Ethane	C₂H₆
3	Propane	C₃H₈
4	Butane	C₄H₁₀

Science, class X (NCERT 2025 ed.), Chapter 4, p.64

While alkanes are generally inert, they aren't completely dormant. In the presence of sunlight, they can undergo a substitution reaction. For example, chlorine can replace hydrogen atoms one by one in a very fast reaction Science, class X (NCERT 2025 ed.), Chapter 4, p.71. This is a key chemical property to remember: alkanes don't 'add' new atoms (like unsaturated fats do during hydrogenation); they 'swap' them.

Sources: Science, class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.60, 64, 65, 71

3. Biofuels and National Biofuel Policy (exam-level)

Biofuels are liquid or gaseous fuels produced from biomass (organic matter such as plant materials and animal waste). In India, an everyday example is Gobar Gas (Biogas), produced through the anaerobic decomposition of cattle dung. The primary combustible constituent of biogas is Methane (CH₄), which typically comprises 50% to 75% of its volume, making it a highly efficient and cleaner alternative to traditional fuels Science, Class X (NCERT), Chapter 4, p.60. From a geographical perspective, while Uttar Pradesh holds the highest potential for biogas production, Maharashtra currently leads in actual production output Geography of India, Majid Husain, Energy Resources, p.30.

To streamline the transition to renewable energy, the government launched the National Policy on Biofuels (2018). A critical feature of this policy is the categorization of biofuels into 'Basic Biofuels' (First Generation or 1G) and 'Advanced Biofuels' (Second Generation or 2G, and Third Generation or 3G). This distinction allows the government to provide targeted incentives, such as Viability Gap Funding (VGF) and off-take assurances, specifically for advanced biofuels like 2G ethanol Indian Economy, Nitin Singhania, Chapter 15, p.453.

Generation	Source Material	Examples
1G (Basic)	Food-based crops (Sugars/Starches)	Sugarcane juice, Corn, Wheat
2G (Advanced)	Non-food biomass & Agricultural waste	Rice straw, Corn cobs, Wood chips
3G (Advanced)	Specially grown aquatic organisms	Algae

One of the policy's most significant achievements is expanding the list of eligible feedstocks for ethanol production. To ensure food security, the policy allows the use of materials unfit for human consumption, including damaged food grains (broken rice, wheat), rotten potatoes, sugar beet, sweet sorghum, and cassava Indian Economy, Nitin Singhania, Chapter 15, p.453. Most recently, in June 2023, the government amended the policy to advance the target of 20% ethanol blending in petrol (E20) to the Ethanol Supply Year (ESY) 2025-26, moving it up five years from the original 2030 deadline Environment, Shankar IAS Academy, India and Climate Change, p.316.

Sources: Science, Class X (NCERT), Chapter 4: Carbon and its Compounds, p.60; Geography of India, Majid Husain, Energy Resources, p.30; Indian Economy, Nitin Singhania, Chapter 15: Infrastructure, p.453; Environment, Shankar IAS Academy, India and Climate Change, p.316

4. Gaseous Fuels: LPG vs CNG vs PNG (intermediate)

To understand the gaseous fuels we use daily, we must first look at their chemical "DNA." Most gaseous fuels are hydrocarbons—compounds made entirely of carbon and hydrogen. The simplest of these is Methane (CH₄), which consists of one carbon atom bonded to four hydrogen atoms Science, class X (NCERT 2025 ed.), Chapter 4, p.60. As we add more carbon atoms to the chain, we get Ethane (C₂H₆), Propane (C₃H₈), and Butane (C₄H₁₀) Science, class X (NCERT 2025 ed.), Chapter 4, p.64. The specific mixture of these molecules determines whether the fuel is LPG, CNG, or Biogas.

Natural Gas (which includes both CNG and PNG) and Biogas (Gobar Gas) share a common hero: Methane. In Natural Gas, methane typically accounts for 80% to 90% of the volume Environment and Ecology, Majid Hussain, Distribution of World Natural Resources, p.15. Similarly, Biogas—produced through the anaerobic decomposition of organic waste like cattle dung—contains 50% to 75% methane Contemporary India II: Textbook in Geography for Class X, Chapter 5, p.117. Because methane is a small, light molecule, it burns cleanly, making it an excellent choice for environmental sustainability.

LPG (Liquefied Petroleum Gas), however, is a different chemical beast. Unlike the methane-heavy natural gas, LPG is composed primarily of Propane and Butane. These are heavier molecules that can be easily liquefied under moderate pressure, which is why they are stored in the heavy steel cylinders we use for domestic cooking. While CNG (Compressed Natural Gas) is methane stored at very high pressure and PNG (Piped Natural Gas) is methane delivered via pipelines, LPG provides a higher energy density per unit of volume due to its heavier molecular structure.

Fuel Type	Primary Constituent	Common Use
CNG / PNG	Methane (CH₄)	Transport (CNG), Household kitchens (PNG)
Biogas (Gobar Gas)	Methane (CH₄)	Rural cooking and lighting
LPG	Propane & Butane	Domestic cooking cylinders

Sources: Science, class X (NCERT 2025 ed.), Chapter 4: Carbon and its Compounds, p.60, 64; Environment and Ecology, Majid Hussain, Distribution of World Natural Resources, p.15; Contemporary India II: Textbook in Geography for Class X, Chapter 5: Minerals and Energy Resources, p.117

5. Government Schemes: GOBAR-dhan and SATAT (exam-level)

At the intersection of rural development and renewable energy lie two pivotal schemes: GOBAR-dhan and SATAT. To understand them, we must first look at the chemistry of biogas. Produced through the anaerobic decomposition (breakdown in the absence of oxygen) of organic matter like cattle dung, agricultural residue, and food waste, biogas is primarily composed of Methane (CH₄), which typically accounts for 50% to 75% of its volume Science Class X (NCERT), Chapter 4, p.60. The remaining portion consists of Carbon Dioxide (CO₂), moisture, and trace amounts of Hydrogen Sulfide (H₂S). Unlike natural gas, which contains ethane and propane, biogas is a cleaner, renewable alternative that prevents the potent greenhouse gas methane from escaping into the atmosphere by capturing it for fuel Indian Economy, Nitin Singhania, Chapter 15, p.452.

The GOBAR-dhan (Galvanizing Organic Bio-Agro Resources Dhan) scheme was launched under the Swachh Bharat Mission (Gramin) to manage biodegradable waste and convert it into energy and organic manure. This creates a circular economy where 'waste' becomes 'wealth' for farmers. The government has committed to establishing 500 new 'waste to wealth' plants to scale this initiative Indian Economy, Vivek Singh, Budget and Economic Survey, p.447. Beyond gas, the byproduct — bio-slurry — is a nutrient-rich organic fertilizer that improves soil aeration and root penetration, reducing the need for chemical inputs Indian Economy, Nitin Singhania, Agriculture, p.310.

While GOBAR-dhan focuses on rural waste management, the SATAT (Sustainable Alternative Towards Affordable Transportation) initiative, led by the Ministry of Petroleum and Natural Gas, aims to mainstream Compressed Bio-Gas (CBG) for the transport sector. By purifying and compressing biogas to remove CO₂ and H₂S, it reaches a methane content of over 95%, making it chemically identical to CNG (Compressed Natural Gas). This allows it to be used in vehicles and industrial applications, reducing India's reliance on imported crude oil and natural gas Geography of India, Majid Husain, Energy Resources, p.13.

Feature	GOBAR-dhan	SATAT
Primary Objective	Rural sanitation and waste-to-wealth for farmers.	Providing affordable, green fuel for transportation.
Nodal Ministry	Ministry of Jal Shakti (Dept. of Drinking Water & Sanitation).	Ministry of Petroleum and Natural Gas (MoPNG).
End Product	Biogas and Bio-slurry (organic fertilizer).	Compressed Bio-Gas (CBG) as an alternative to CNG.

Sources: Science Class X (NCERT), Chapter 4: Carbon and its Compounds, p.60; Indian Economy, Nitin Singhania, Chapter 15: Infrastructure, p.452; Indian Economy, Vivek Singh, Budget and Economic Survey, p.447; Indian Economy, Nitin Singhania, Agriculture, p.310; Geography of India, Majid Husain, Energy Resources, p.13

6. The Process of Anaerobic Digestion (intermediate)

Anaerobic digestion is a biological process in which microorganisms break down biodegradable material in the absence of oxygen. In the context of rural India, this process is most commonly seen in Gobar Gas plants, where cattle dung, crop residues, and human waste are converted into useful energy NCERT Contemporary India II, Chapter 5, p.117. Unlike aerobic composting, which requires air to decompose organic matter, anaerobic digestion takes place in a sealed environment (a digester) where specific bacteria, known as methanogens, thrive and process the waste. During this decomposition, the organic matter undergoes a chemical transformation that significantly lowers the C:N (Carbon to Nitrogen) ratio of the refuse, making the resulting byproduct an excellent fertilizer Shankar IAS Academy Environment, Agriculture, p.364. The gas produced is a mixture, with Methane (CH₄) being the primary combustible component (typically 50-75%), alongside Carbon Dioxide (CO₂) and trace amounts of other gases. This methane-rich biogas is prized for its high thermal efficiency, providing more heat energy per unit compared to traditional fuels like kerosene, dung cakes, or charcoal NCERT Contemporary India II, Chapter 5, p.117. This process offers what experts call "twin benefits": it provides a clean, renewable source of energy for cooking and lighting, while simultaneously producing high-quality organic manure (slurry). Because of these advantages, the Government of India has historically supported the installation of millions of family-type biogas plants under initiatives like the National Biogas and Manure Management Programme (NBMMP), managed by the Ministry of New and Renewable Energy Nitin Singhania Indian Economy, Chapter 15, p.453.

Feature	Anaerobic Digestion (Biogas)	Traditional Burning (Dung Cakes)
Oxygen Required	No (Oxygen-free)	Yes (Combustion)
Primary Output	Methane (CH₄) + Organic Manure	Heat + Ash + Smoke (CO, Particulates)
Energy Efficiency	High Thermal Efficiency	Low Thermal Efficiency
Environment	Reduces Greenhouse Gas emissions	Produces indoor air pollution

Sources: NCERT Contemporary India II, Chapter 5: Mineral and Energy Resources, p.117; Shankar IAS Academy Environment, Agriculture, p.364; Nitin Singhania Indian Economy, Chapter 15: Infrastructure, p.453; NCERT Science Class X, Chapter 4: Carbon and its Compounds, p.60

7. Chemical Composition of Biogas (Gobar Gas) (basic)

Biogas, affectionately known as Gobar Gas in rural India, is a remarkable example of green chemistry in action. It is produced through the anaerobic decomposition (breakdown without oxygen) of organic matter such as cattle dung, farm waste, and shrubs Contemporary India II: Textbook in Geography for Class X, Chapter 5, p.117. This process yields a gaseous mixture that serves as a highly efficient fuel for cooking and lighting, offering much higher thermal efficiency than burning traditional dung cakes or charcoal.

The chemical identity of biogas is defined by two major players and a few minor ones. The most significant constituent is Methane (CH₄), which typically makes up 50% to 75% of the total volume. Methane is the primary combustible component that makes biogas such an effective energy source. The second major component is Carbon Dioxide (CO₂), accounting for about 25% to 50%. While methane provides the energy, the presence of carbon dioxide acts as a diluent. You might also find trace amounts of Hydrogen Sulfide (H₂S), which gives raw biogas a distinct smell, and moisture Science, Class X (NCERT), Chapter 4, p.60.

It is important to distinguish biogas from the Earth's atmosphere or Natural Gas. While our atmosphere is dominated by Nitrogen (78%) and Oxygen (21%) Physical Geography by PMF IAS, Earths Atmosphere, p.271, biogas is almost entirely composed of Carbon and Hydrogen compounds. Furthermore, unlike Natural Gas, which contains heavier hydrocarbons like ethane and propane, biogas is essentially a "cleaner" mixture of simple methane and carbon dioxide.

Component	Percentage (Approx.)	Role
Methane (CH₄)	55 - 75%	Primary fuel / Combustible part
Carbon Dioxide (CO₂)	25 - 45%	Non-combustible byproduct
Traces (N₂, H₂S, H₂)	1 - 5%	Impurity / Trace gases

Sources: Contemporary India II: Textbook in Geography for Class X, Chapter 5: Minerals and Energy Resources, p.117; Science, Class X (NCERT), Chapter 4: Carbon and its Compounds, p.60; Physical Geography by PMF IAS, Earths Atmosphere, p.271

8. Solving the Original PYQ (exam-level)

You have just mastered the concepts of carbon bonding and anaerobic decomposition, and this question is the perfect application of those building blocks. In your study of organic chemistry, you learned that when organic matter—like cattle dung—breaks down in the absence of oxygen, it undergoes a fermentation process. This biological process, as detailed in Science, class X (NCERT 2025 ed.), primarily produces the simplest hydrocarbon, which acts as a high-efficiency fuel. By connecting the dots between waste management and renewable energy, you can see that the goal of a biogas plant is to capture this specific combustible gas.

To arrive at the correct answer, evaluate the composition percentages you encountered in your readings. While biogas is a mixture, Methane is the dominant player, accounting for 50% to 75% of the total volume. When a UPSC question asks for the "main constituent," it is looking for the element that provides the primary functional value—in this case, the heating power. As highlighted in Contemporary India II: Textbook in Geography for Class X, this high methane content is what makes gobar gas a superior alternative to traditional fuels like charcoal or dung cakes. Therefore, (B) Methane is the only logical conclusion.

It is crucial to avoid the common traps set by the other options. Ethane and Propane are often included to confuse you with Natural Gas or LPG (Liquefied Petroleum Gas); while these are hydrocarbons, they are typically sourced from fossil fuel deposits rather than the rapid decomposition of animal waste. Acetylene is another distractor, primarily used in industrial welding and not produced in significant quantities through biological decay. Always distinguish between biological fuels (Biogas) and geological fuels (Natural Gas) to steer clear of these recurring UPSC decoys.