Alkanes MCQ for NEET

Explanation: The question asks what compound is formed when acetic Acid reacts with ethyl Alcohol in the presence of concentrated sulphuric Acid. This is a classic reaction between a carboxylic Acid and an Alcohol. Concentrated sulphuric Acid (H₂SO₄) acts as a catalyst and also as a dehydrating agent, removing water formed during the reaction. The –OH group from the Acid and a hydrogen Atom from the Alcohol combine to form water (H₂O), while the remaining parts join to produce a new compound with a characteristic fruity smell. Such reactions are widely used in preparing flavouring agents and fragrances in laboratories and industries.
Hint: Recall the reaction between a carboxylic Acid and an Alcohol that produces a pleasant-smelling compound along with water (H₂O).

Explanation: This question asks which pair of compounds have the same Molecular formula but differ in their structural arrangement. Isomers are substances that contain identical numbers of atoms of each element but differ in the way those atoms are connected. To identify isomers, first compare their Molecular formulas, such as C₄H₁₀. If the formulas differ, they cannot be isomers. If the formulas are the same, then check whether one compound has a straight-chain structure while the other has a branched arrangement. Such structural differences lead to variations in physical properties, even though the overall Molecular composition remains identical.
Hint: Look for two compounds that share the same Molecular formula (for example, C₄H₁₀) but differ in structural arrangement.

Explanation: This question asks how acetic acid (CH₃COOH) is prepared from common laboratory or industrial methods. Acetic acid is a simple carboxylic acid that can be formed by controlled oxidation of certain Alcohols. Primary Alcohols, when oxidized, first form aldehydes and then further oxidize to carboxylic Acids. Ethanol (C₂H₅OH) undergoes oxidation to form ethanoic acid. This reaction may occur chemically using oxidizing agents or biologically with the help of microorganisms in the presence of oxygen. The key idea is that increasing oxygen content converts Alcohol into acid.
Hint: Think about the oxidation of a primary Alcohol like ethanol leading to a carboxylic acid.

Explanation: This question focuses on the conditions required for chlorine to react with saturated Hydrocarbons (alkanes). Alkanes are relatively unreactive because they contain only single bonds. However, in the presence of ultraviolet Light or sunlight, chlorine molecules split into free radicals. These free radicals initiate a substitution reaction in which hydrogen atoms in the alkane are replaced by chlorine atoms. Without Light, the reaction proceeds very slowly or not at all. Thus, Light provides the necessary energy to start the chain reaction mechanism.
Hint: Consider what helps chlorine molecules break into reactive free radicals.

Explanation: Graphite and diamond are allotropes of carbon, meaning they are different structural forms of the same element. Although they differ in hardness, density, and electrical conductivity, their chemical composition is identical. Both consist entirely of carbon atoms. Because they are made of the same element, they undergo similar chemical reactions under comparable conditions, such as combustion to form carbon dioxide (CO₂). Their differences arise from Bonding arrangements, not from chemical composition.
Hint: Focus on what remains common between graphite and diamond despite their structural differences.

Explanation: The question compares methanol (CH₃OH) and ethanol (C₂H₅OH). By examining their Molecular formulas, we notice that ethanol has one extra carbon Atom and two extra hydrogen atoms compared to methanol. This difference represents a –CH₂ unit, which has a Molecular Mass of 14 units (12 for carbon and 2 for hydrogen). This pattern is characteristic of homologous series, where successive members differ by a –CH₂ group.
Hint: Subtract the smaller Alcohol formula from the larger one and identify the repeating unit.

Explanation: To identify the common feature, examine the relationship between carbon and hydrogen atoms in each compound. Many Hydrocarbons follow specific general formulas depending on whether they are alkanes, alkenes, or alkynes. By comparing the number of hydrogen atoms relative to carbon atoms, we observe that several of these compounds follow the same mathematical relationship between C and H. Even if the number of carbon atoms changes, the pattern remains consistent. This indicates they belong to the same general formula category.
Hint: Check whether the hydrogen atoms follow a consistent mathematical relation with carbon atoms.

Explanation: When an alcohol reacts with a carboxylic acid in the presence of a catalyst like concentrated H₂SO₄, they combine to form a compound with a pleasant fruity smell along with water. This reaction involves removal of a water Molecule and formation of a new linkage between the acid and alcohol. It is widely used in Organic Chemistry for synthesizing flavouring agents. The reaction has a specific name distinct from combustion or hydrolysis reactions.
Hint: Recall the name of the reaction that produces sweet-smelling compounds from Acids and Alcohols.

Explanation: Many fruits owe their aroma and flavour to Organic compounds such as esters and Alcohols. These volatile substances evaporate easily and stimulate our sense of smell. In apples, a particular Organic compound contributes significantly to the familiar fruity aroma. Such compounds are often formed through natural biochemical processes inside the fruit during ripening. The key idea is that fruit flavours are usually due to small Organic molecules with distinct smells.
Hint: Think of a simple Organic compound commonly found in fermented or fruit-related products.

Explanation: Nail polish remover requires a solvent capable of dissolving resins and synthetic Polymers present in nail varnish. A suitable solvent must evaporate quickly and effectively dissolve Organic compounds. One commonly used solvent in cosmetic products fits these properties. It is a volatile Organic compound widely used in laboratories and industries for cleaning and dissolving substances.
Hint: Consider a fast-evaporating Organic solvent frequently used in laboratories.

Explanation: A sooty flame is produced when compounds with a high carbon-to-hydrogen ratio burn incompletely. Aromatic Hydrocarbons like benzene and polycyclic compounds tend to produce soot because of their higher carbon content. In contrast, saturated Hydrocarbons (alkanes) have a lower carbon-to-hydrogen ratio and burn more cleanly, producing a non-sooty flame. Therefore, the compound with a simpler saturated structure is less likely to produce soot during combustion.
Hint: Choose the compound that is a saturated hydrocarbon with a lower carbon-to-hydrogen ratio.

Explanation: Vinegar is essentially dilute acetic acid formed by the oxidation of ethanol. Certain bacteria facilitate this conversion in the presence of oxygen. These microorganisms belong to a specific genus that oxidizes alcohol into acetic acid during fermentation. This biological process is used in vinegar production worldwide. The organism acts as a catalyst for the oxidation process rather than as a chemical reagent.
Hint: Recall the bacteria involved in the biological oxidation of alcohol to acetic acid.

Explanation: Glacial acetic acid refers to a highly concentrated form of acetic acid (CH₃COOH). The term “glacial” comes from its property of solidifying into ice-like crystals at about 16.6°C. Unlike dilute vinegar solutions, this form contains almost no water and represents the pure compound. Because it is nearly 100% acetic acid, it is more corrosive and has stronger chemical properties compared to its diluted form. In laboratories and industries, glacial acetic acid is used where a water-free reagent is required for controlled chemical reactions.
Hint: Focus on the concentration and absence of water in this special form of acetic acid.

Explanation: Graphite is an allotrope of carbon in which each carbon Atom is bonded to three others in layered hexagonal sheets. These layers slide over one another, making graphite soft and slippery. It appears black and is used in pencils and lubricants. Graphite also has a very high melting point due to strong covalent Bonding within layers. Compared to diamond, its density is slightly lower but not drastically different. Therefore, any statement contradicting these established physical properties would be incorrect.
Hint: Think about graphite’s density and melting point compared to diamond.

Explanation: A heteroatom in Organic Chemistry is any Atom other than carbon and hydrogen present in a carbon chain. In the given compound, carbon (C) and hydrogen (H) form the main backbone. However, the Molecule also contains oxygen (O) and chlorine (Cl). Since heteroatoms are defined as atoms different from carbon and hydrogen within an Organic compound, oxygen and chlorine qualify as heteroatoms in this structure. Their presence influences chemical reactivity and polarity of the compound.
Hint: Identify atoms in the structure that are neither carbon nor hydrogen.

Explanation: A quaternary (4°) carbon Atom is one that is directly bonded to four other carbon atoms. In 2,2,4,4-tetramethylpentane, the main pentane chain has additional methyl (–CH₃) groups attached at positions 2 and 4. At each of these positions, the central carbon becomes bonded to four carbon atoms: two from the main chain and two from methyl substituents. Therefore, each of these positions forms a quaternary carbon. Counting such centers gives the total number of 4° carbon atoms in the Molecule.
Hint: Look at the carbon atoms at positions 2 and 4 and count how many carbons each is attached to.

Explanation: Hydrogenation is a process in which hydrogen (H₂) is added to unsaturated vegetable oils to convert them into more saturated fats. This reaction reduces carbon–carbon double bonds and increases solidity. The reaction requires a metal catalyst to proceed efficiently. A commonly used catalyst in industrial hydrogenation is a finely divided transition metal that provides a surface for hydrogen molecules to react with the oil. This catalyst enables the addition of hydrogen across double bonds under controlled conditions.
Hint: Think of the commonly used metal catalyst in industrial hydrogenation of oils.

Explanation: Marsh gas is a naturally occurring gas produced by the decomposition of organic Matter in marshy or swampy areas under anaerobic (oxygen-free) conditions. Microorganisms break down plant and Animal Matter, releasing a simple hydrocarbon gas. This gas is the main component of biogas and is also found in natural gas reserves. Chemically, it is the simplest alkane with the formula CH₄.
Hint: Recall the simplest alkane that forms naturally in swamps and biogas.

Explanation: A homologous series is a family of organic compounds with the same functional group and similar chemical properties, where successive members differ by a –CH₂ unit. Examples include Alcohols, carboxylic Acids, aldehydes, ketones, and haloalkanes. Each series has a general formula and shows gradual changes in physical properties such as boiling point. The key feature is the presence of a common functional group and a repeating structural pattern among members.
Hint: Focus on groups that share a common functional group and differ by a –CH₂ unit.

Explanation: Isomerism refers to the phenomenon where compounds have the same molecular formula but differ in structural arrangement or spatial configuration. Because of these structural differences, isomers may exhibit different chemical and physical properties even though their molecular composition is identical. For example, structural isomers differ in Bonding arrangement, while stereoisomers differ in spatial orientation. The concept explains why compounds with identical formulas can behave differently in reactions.
Hint: Think about how identical molecular formulas can still lead to differences in structure and properties.