Hydrocarbons

Concept: Autotrophic nutrition is a mode of nutrition where an organism produces its own food from simple inorganic substances, typically using an external energy source. The most common form is photosynthesis, used by plants, algae, and some bacteria. Step 1: Understanding Photosynthesis (the primary autotrophic process) Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods (glucose) from carbon dioxide and water. Chlorophyll is the green pigment that captures light energy. The overall simplified chemical equation for photosynthesis is: Step 2: Identifying the essential requirements for photosynthesis From the equation and process description, the key requirements are:
Carbon Dioxide ( ): Obtained from the atmosphere. Provides the carbon atoms for glucose.
Water ( ): Absorbed from the soil (by plants) or surrounding environment. Provides hydrogen atoms for glucose and is the source of oxygen released.
Sunlight (Light Energy): Provides the energy to drive the chemical reactions.
Chlorophyll: The green pigment found in chloroplasts of plant cells (and in photosynthetic bacteria). It absorbs light energy. Step 3: Analyzing the options
(1) , sunlight, red pigment and : (sulfur dioxide) is not a primary reactant for typical plant photosynthesis. "Red pigment" is incorrect; chlorophyll (green) is primary, though other accessory pigments exist.
(2) , sunlight, chlorophyll and : This option correctly lists all the essential requirements for photosynthesis in green plants. Correct.
(3) , sunlight, chlorophyll and : (oxygen) is a {product} of photosynthesis, not a requirement. (hydrogen gas) is not a direct input in this form for plant photosynthesis (hydrogen comes from water).
(4) None of the above: Incorrect, as option (2) is correct. Therefore, the autotrophic mode of nutrition (specifically photosynthesis) requires carbon dioxide, sunlight, chlorophyll, and water.

Concept: Carbon is unique in its ability to form a vast number of compounds. This is due to specific properties of the carbon atom. Step 1: Key Properties of Carbon leading to many compounds \begin{enumerate} % Option (q) Catenation: This is the ability of an element to form long chains and rings by bonding to itself. Carbon exhibits catenation to a remarkable extent, forming stable carbon-carbon bonds. These chains and rings can be of various lengths and structures (straight, branched). % Option (r) Tetravalency: Carbon has four valence electrons, allowing it to form four covalent bonds with other atoms (including other carbon atoms or atoms of different elements like hydrogen, oxygen, nitrogen, halogens). % Option (s) Ability to form multiple bonds: Carbon can form single ( ), double ( ), and triple ( ) bonds with itself and other elements, further increasing the variety of possible structures. % Option (t) Isomerism: The ability of compounds with the same molecular formula to exist in different structural arrangements, leading to different properties. This is enabled by carbon's bonding versatility. The question asks for {the} property responsible for a {large number} of organic compounds. While tetravalency and multiple bonding are essential, catenation is the primary reason for the sheer number and diversity of carbon chains and rings that form the backbone of organic molecules. Step 2: Analyzing the options
(1) Allotropy: This is the property of some chemical elements to exist in two or more different forms (allotropes) in the same physical state. For example, carbon exists as diamond, graphite, fullerenes, etc. While carbon shows allotropy, this property itself doesn't explain the vast number of {different organic compounds} (which involve carbon bonded to other elements as well).
(2) Catenation: This self-linking property of carbon to form long chains, branched chains, and rings is a fundamental reason for the immense diversity and large number of organic compounds.
(3) Hybridisation ( ): This is a concept that explains the geometry and bonding of carbon atoms (e.g., tetrahedral, trigonal planar, linear shapes). Hybridisation enables carbon to form its diverse bonds and structures, supporting catenation and tetravalency, but catenation is the more direct answer to "property responsible for a large number."
(4) None of these: Incorrect, as catenation is a key property. Step 3: Identifying the primary property Catenation is the most direct and significant property of carbon that accounts for the formation of a vast number of organic compounds.

Concept: Historically, organic compounds were believed to be produced only by living organisms due to a "vital force." The laboratory synthesis of an organic compound from inorganic starting materials was a landmark event that disproved this theory. Step 1: The Vital Force Theory In the early 19th century, the prevailing "vital force theory" (vitalism) suggested that organic compounds could only be formed by living organisms because they possessed a special "vital force." Step 2: Friedrich Wöhler's Experiment (1828) In 1828, the German chemist Friedrich Wöhler made a groundbreaking discovery. He was attempting to synthesize ammonium cyanate ( ), an inorganic compound. He did this by reacting silver cyanate ( ) with ammonium chloride ( ), or potassium cyanate with ammonium sulfate. Upon heating ammonium cyanate, he unexpectedly obtained crystals of urea ( ). Urea was a known organic compound, found in urine. Wöhler's synthesis of urea from an inorganic starting material (ammonium cyanate was considered inorganic) was the first time an organic compound was synthesized in the laboratory without the involvement of living organisms. Step 3: Significance of Wöhler's Synthesis This experiment was a major blow to the vital force theory and paved the way for the development of modern organic chemistry, which is based on the understanding that the same chemical principles govern both organic and inorganic compounds. Step 4: Analyzing the options % Option (X) (1) Methane ( ): While a simple organic compound, it was not the first synthesized in this landmark context. % Option (Y) (2) Urea ( ): This is the correct answer, synthesized by Wöhler in 1828. % Option (Z) (3) Thiourea ( ): A derivative of urea, but not the first synthesized. % Option ([) (4) Ethanol ( ): Known through fermentation for millennia, but its synthesis from purely inorganic precursors in a lab was not the first breakthrough against vitalism.

Step 1: Understand the concept of homologous series.
In organic chemistry, a homologous series is a series of compounds with the same general formula, usually varying by a single parameter such as the length of a carbon chain. All compounds in a homologous series have the same functional group and similar chemical properties, with a gradual change in physical properties as the series progresses. Step 2: Identify the difference between successive members of a homologous series.
Successive compounds in a homologous series differ by a -CH (methylene) unit. For example, in the alkane series:
Methane (CH )
Ethane (C H ) - differs from methane by one -CH group (CH + CH = C H )
Propane (C H ) - differs from ethane by one -CH group (C H + CH = C H ) This pattern holds true for other homologous series as well (e.g., alcohols, carboxylic acids, etc.), as long as they have the same functional group. Step 3: Compare the conclusion with the given options.
The difference between two successive compounds having the same functional group is a -CH unit. This corresponds to option (1). $ _2 $

Step 1: Understand the definition of a functional group.
A functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. Step 2: Recall the common functional groups and their formulas.
Aldehyde group: -CHO (or -CH=O)
Carboxylic acid group: -COOH (or -C(=O)OH)
Ketone group: -C(=O)- (often shown within a molecule like -COCH for a methyl ketone, but the group itself is just the carbonyl carbon bonded to two other carbons)
Hydroxyl group (Alcohol): -OH Step 3: Identify the formula for the Carboxylic group.
Based on the recall, the carboxylic group is characterized by a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl (-OH) group. Its formula is -COOH. Step 4: Compare the conclusion with the given options.
Option (2) -COOH correctly represents the carboxylic group. $ $