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The correct answer is Na.

Key Points

• Sodium (Na) is widely extracted by the electrolysis of its molten compound, specifically molten sodium chloride (NaCl), also known as rock salt.
• The process used for sodium extraction is called the Downs Cell Method, where molten NaCl is electrolyzed to produce metallic sodium at the cathode and chlorine gas at the anode.
• Electrolysis is required for sodium extraction because of its high reactivity; it cannot be reduced using carbon or other chemical methods.
• Sodium is highly reactive and belongs to the alkali metal group in the periodic table. It is used in various industries, including chemical manufacturing and metallurgy.
• The melting point of sodium chloride is lowered by adding calcium chloride (CaCl₂) during electrolysis to make the process more efficient.

Additional Information

• Copper (Cu):
• Copper is primarily extracted from its ores, such as chalcopyrite (CuFeS₂), through pyrometallurgical processes like roasting, smelting, and refining, rather than electrolysis of its molten compound.
• Electrolysis is used for the purification of copper in electrolytic refining, not for extraction.
• Copper is a good conductor of electricity and widely used in electrical wiring, electronics, and plumbing.
• Gold (Au):
• Gold is not extracted through electrolysis of its molten compound; it is primarily extracted from ores like gold-bearing quartz through processes such as cyanidation and amalgamation.
• Gold is highly unreactive and occurs in its native state in nature, making it easier to extract without complex methods.
• It is used for jewelry, electronics, and as a standard for monetary systems.
• Tin (Sn):
• Tin is extracted from its main ore, cassiterite (SnO₂), using reduction methods involving carbon in a blast furnace.
• Electrolysis is not used for tin extraction because tin oxide can be readily reduced to metallic tin using carbon.
• Tin is widely used for coating other metals to prevent corrosion, as well as in the production of alloys like bronze.
• Electrolysis:
• Electrolysis is a chemical process that uses electric current to drive the decomposition of compounds into their constituent elements.
• It is particularly useful for extracting highly reactive metals like sodium, potassium, and aluminum, which cannot be extracted by conventional reduction methods.
• Molten electrolytes or aqueous solutions are used depending on the compound and metal involved.

The correct answer is 4) It is a wide band-gap semiconductor.

Key Points

• Graphene is not a wide band-gap semiconductor; instead, it is a zero band-gap material. This makes it unique and distinct from traditional semiconductors.
• Due to its zero band-gap property, graphene has exceptional electrical conductivity, which allows electrons to move freely without any resistance.
• The absence of a band-gap limits its application in electronic devices where switching capabilities (on-off states) are crucial.
• Efforts are being made in research to induce a band-gap in graphene to make it suitable for semiconductor applications.

Additional Information

• It is the thinnest material known so far:
• Graphene is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice.
• It is only one atom thick, making it the thinnest material ever discovered.
• Despite its thinness, graphene is incredibly strong, with a tensile strength 200 times greater than steel.
• It is almost completely transparent:
• Graphene absorbs only about 2-3% of visible light, making it nearly transparent.
• This property makes it suitable for applications such as transparent conductive coatings, touchscreens, and optical devices.
• It is highly conducting:
• Graphene exhibits exceptional electrical conductivity due to the free movement of electrons within its structure.
• It is considered one of the best conductors of electricity, even outperforming copper.
• This property is attributed to its zero band-gap and unique electronic structure.

The correct answer is They have strong covalent bonds. Key Points

Plastics are made of long chains of polymers that are held together by strong covalent bonds, which are difficult to break down naturally. These covalent bonds impart durability and resistance to environmental factors, such as moisture and temperature changes, preventing easy degradation. Microorganisms and enzymes in the environment usually cannot break down these strong bonds, making plastics non-biodegradable. The chemical structure of plastics, with repetitive units, makes them resistant to biological processes like decomposition. Due to their persistence in the environment, plastics contribute to long-term pollution if not disposed of or recycled properly.

Additional Information

Option 1: They have strong ionic bonds

Plastics are not made of ionic bonds. Ionic bonds are typically found in compounds formed between metals and non-metals, such as sodium chloride. Ionic compounds dissolve in water or break down under specific conditions, unlike plastics which are insoluble and durable.

Option 3: They have strong metallic bonds

Metallic bonds are found in metals and alloys, where free electrons move within a lattice of positive ions, giving metals properties like conductivity and malleability. Plastics do not have metallic bonds as they are composed of carbon-based polymers, not metals.

Option 4: They have very high melting points (> 500°C)

While some plastics have high melting points, this is not the primary reason for their resistance to degradation. The inability of microorganisms to break the strong covalent bonds in plastics is the main cause of their non-degradability, not their melting point.

Main Theme: Why plastics do not degrade easily

Plastics are synthetic materials derived from petrochemicals, designed to be durable and resistant to environmental degradation. Efforts are being made to develop biodegradable plastics that can be broken down by microorganisms to address environmental concerns. Proper recycling and disposal methods are essential to mitigate the environmental impact of non-degradable plastics.

The correct answer is C2H5COOH.

Key Points

• C2H5COOH is the correct formula for propanoic acid, which is a type of carboxylic acid. The functional group in carboxylic acids is –COOH.
• Carboxylic acids contain a hydroxyl group (-OH) attached to a carbon atom that is also part of a carbonyl group (C=O), forming the carboxyl group (-COOH).
• The general formula for carboxylic acids is R-COOH, where "R" is an alkyl or aryl group, and the -COOH group defines its chemical properties.
• Propanoic acid (C2H5COOH) is widely used in the food industry as a preservative and is also involved in chemical synthesis.
• Carboxylic acids exhibit acidic properties due to the ability of the -COOH group to donate a proton (H+) in aqueous solutions, forming a carboxylate ion (R-COO⁻).

Additional Information

• Option 1: C3H7OH
• This is the chemical formula for propanol, which belongs to the alcohol functional group.
• Alcohols are characterized by the presence of the hydroxyl (-OH) group attached to a saturated carbon atom.
• Propanol is not a carboxylic acid; it does not have the -COOH group and does not exhibit acidic properties.
• Option 2: C3Hg
• This formula is chemically incorrect and does not represent any valid organic or inorganic compound.
• It does not align with the structural framework of carboxylic acids or any related functional group.
• Option 4: CH3COCH3
• This is the chemical formula for acetone, which is a ketone and not a carboxylic acid.
• Ketones are characterized by the presence of a carbonyl group (C=O) bonded to two carbon atoms.
• Acetone is a common solvent used in laboratories and industries, but it does not contain the -COOH group that defines carboxylic acids.
• Main Theme: Carboxylic Acids
• Carboxylic acids are an important class of organic compounds with diverse applications in industries, including food preservation, pharmaceuticals, and polymer production.
• They exhibit unique properties such as high boiling points due to hydrogen bonding and acidic behavior in aqueous solutions.
• Examples include formic acid (HCOOH), acetic acid (CH3COOH), and benzoic acid (C6H5COOH).

The correct answer is It has six isomers.

Key Points

• Benzene is a symmetrical molecule with the chemical formula C6H6, and due to its symmetry, it does not have six isomers.
• The structure of benzene features a single unique arrangement of its carbon and hydrogen atoms, with delocalized electrons forming a conjugated pi-system.
• Isomers are compounds with the same molecular formula but different arrangements of atoms. Benzene’s fixed ring structure eliminates the possibility of such variations.
• Some derivatives of benzene (e.g., toluene, xylene) have isomers, but pure benzene itself does not.
• Therefore, the statement "It has six isomers" is incorrect.

Additional Information

• Each carbon atom forms sigma bonds with two other carbon atoms with a bond angle of 120°:
• Benzene has a hexagonal planar structure, and each carbon atom is sp2 hybridized, forming sigma bonds with two adjacent carbon atoms and one hydrogen atom.
• The bond angle in benzene is 120°, characteristic of trigonal planar geometry, ensuring a symmetrical arrangement.
• Delocalized electrons create a symmetrical 'cloud' of electrons above and below the plane:
• Benzene’s structure is stabilized by the delocalization of six pi-electrons over the entire ring.
• This delocalization creates a symmetrical electron cloud above and below the planar ring, which contributes to benzene’s aromaticity and high stability.
• The length of C-C bonds is intermediate between single and double bonds:
• In benzene, all carbon-carbon bond lengths are equal and measure approximately 1.39 Å, which is intermediate between the typical single bond (1.54 Å) and double bond (1.34 Å).
• This is due to the resonance structure of benzene, where the pi-electrons are shared equally among all six carbon atoms.

The correct answer is N₂.

Key Points

• N₂, or nitrogen gas, is an inert diatomic molecule that is abundant in the atmosphere but does not act as a fertilizer.
• Nitrogen fertilizers are compounds that provide nitrogen in a form plants can absorb, such as ammonium (NH₄⁺) or nitrate (NO₃^-).
• N₂ must be converted into reactive nitrogen compounds through processes like the Haber-Bosch method before plants can utilize it.
• Unlike other options listed, N₂ does not directly contribute to plant nutrition as it is unavailable to plants in its gaseous form.
• Atmospheric nitrogen is fixed into fertilizers through industrial processes or by biological nitrogen fixation by microorganisms.

Additional Information

• (NH₄)₂SO₄ (Ammonium sulfate):
• This is a nitrogen fertilizer that contains 21% nitrogen in the ammonium form and 24% sulfur.
• It is widely used in agriculture to improve nitrogen content in soil and supply sulfur for plant growth.
• Ammonium sulfate is particularly beneficial for acidic soils and crops like rice and wheat.
• NH₄NO₃ (Ammonium nitrate):
• Ammonium nitrate is a dual-purpose nitrogen fertilizer, containing both ammonium (NH₄⁺) and nitrate (NO₃^-).
• It provides readily available nitrogen for plants and is commonly used in agriculture for crops like corn and vegetables.
• Due to its high nitrogen content, it is a key component in boosting crop yield.
• (NH₂)₂CO (Urea):
• Urea is the most widely used nitrogen fertilizer, containing 46% nitrogen—the highest among solid fertilizers.
• It is cost-effective and can be applied directly to soil or mixed with water for foliar application.
• Urea undergoes hydrolysis in soil to release ammonium, which is then converted into nitrate by microorganisms.
• Main Theme:
• Nitrogen fertilizers are essential for plant growth as nitrogen is a vital nutrient for processes like photosynthesis and protein synthesis.
• These fertilizers play a critical role in agriculture, ensuring higher crop yields and food security globally.
• The question highlights the importance of distinguishing between inert nitrogen (N₂) and reactive nitrogen compounds in fertilizers.

The correct answer is (n - 1) d^1–10 ns^0–2.

Key Points

• Transition elements are characterized by the partial filling of the d-orbitals in the (n-1) shell, leading to the general electronic configuration of (n - 1) d^1–10 ns^0–2.
• They are located in the d-block of the periodic table, spanning groups 3 to 12, and exhibit unique properties such as variable oxidation states and the ability to form colored compounds.
• The outermost ns electrons are often lost during chemical reactions, leaving behind partially filled (n-1) d orbitals, which is a defining feature of transition metals.
• Examples of transition metals include iron (Fe), cobalt (Co), and copper (Cu), all of which follow this electronic configuration pattern.
• The involvement of d-orbitals in bonding contributes to properties like high melting points, conductivity, and magnetic behavior in transition metals.

Additional Information

• Option 1 - (n - 2) d^1–10 ns²:
• This configuration represents the electronic structure of inner transition elements, such as lanthanides and actinides, rather than transition metals.
• In these elements, the f-orbitals (n-2) are being filled, while the d-orbitals are either empty or partially filled.
• Option 2 - (n - 2) f^1–14 (n - 1) d^0–1 ns²:
• This configuration is specific to inner transition metals (f-block elements), including lanthanides and actinides.
• In these elements, the (n-2) f-orbitals are progressively filled, and they are not part of the d-block or transition metal category.
• Option 3 - ns² np⁶ nd^1–10:
• This configuration is not correct for transition metals as it includes np⁶, which is characteristic of noble gases with completely filled p-orbitals.
• Transition metals do not have a fully filled np orbital in their ground-state configuration.

The correct answer is Iron.

Key Points

• Iron exhibits variable oxidation states, primarily +2 (ferrous) and +3 (ferric), due to the ability of its d-orbitals to lose electrons.
• Iron can also exhibit oxidation states such as +4, +6, and even +1 in certain complex compounds.
• The variable oxidation states of iron are crucial in its role in biological systems (e.g., hemoglobin) and industrial applications (e.g., catalysts).
• The electronic configuration of iron is [Ar] 3d⁶4s², and the removal of electrons from the 3d and 4s orbitals facilitates its variable oxidation states.
• Iron's ability to change its oxidation state is central to redox reactions, making it vital in processes like corrosion and in the functioning of batteries.

Additional Information

• Sodium:
• Sodium primarily exhibits a fixed oxidation state of +1 due to its single valence electron in the 3s orbital.
• It is an alkali metal belonging to Group 1 of the periodic table, and its reactivity is due to the ease of losing this single electron.
• Sodium is widely used in chemical industries, biological functions (e.g., nerve signaling), and in the production of compounds such as sodium hydroxide and sodium chloride.
• Calcium:
• Calcium exhibits a fixed oxidation state of +2 as it loses two electrons from the 4s orbital.
• It is an alkaline earth metal found in Group 2 of the periodic table.
• Calcium plays critical roles in biological systems, including bone formation, muscle contraction, and enzymatic functions.
• In industrial applications, calcium compounds like calcium carbonate are used in construction and manufacturing.
• Lithium:
• Lithium exhibits a fixed oxidation state of +1 due to the loss of its single valence electron in the 2s orbital.
• It is the lightest metal and belongs to Group 1 of the periodic table.
• Lithium is widely used in rechargeable batteries, psychiatric medications (e.g., lithium carbonate), and as a heat transfer agent.
• Variable Oxidation Numbers:
• Elements with variable oxidation states, such as iron, transition metals, and some p-block elements, are capable of forming multiple types of chemical bonds.
• The ability to exhibit variable oxidation states allows these elements to participate in diverse chemical reactions and complex formation.
• This property is particularly significant in catalysis, coordination chemistry, and biological processes.

The correct answer is Hydrogen sulphide.

Key Points

• Hydrogen sulphide (H₂S) is a colorless gas known for its characteristic odor of rotten eggs.
• This gas is naturally produced through the anaerobic decomposition of organic matter by bacteria, especially in swamps, sewers, and stagnant waters.
• It is highly toxic and flammable, even at low concentrations, and poses significant health and safety risks in industrial settings.
• Hydrogen sulphide exposure can cause irritation to the eyes, nose, and throat at low levels, while higher concentrations can lead to severe respiratory distress or even death.
• It is commonly encountered in industries such as petroleum refining, natural gas processing, and wastewater treatment facilities.

Additional Information

• Ammonia (NH₃)
• Ammonia is a colorless gas with a strong, pungent odor and is widely used in fertilizers and cleaning products.
• It is composed of nitrogen and hydrogen and is highly soluble in water, forming ammonium hydroxide.
• While it does have a strong smell, it does not resemble the odor of rotten eggs.
• Acetylene (C₂H₂)
• Acetylene is a colorless gas with a faint, ether-like odor.
• It is widely used as a fuel for welding and cutting due to its high flame temperature.
• It is not associated with a rotten egg smell.
• Sulphur dioxide (SO₂)
• Sulphur dioxide is a colorless gas with a sharp, suffocating smell, often described as similar to burning matches.
• It is produced from the burning of fossil fuels containing sulfur and is a major air pollutant.
• It does not have the characteristic smell of rotten eggs.
• Main Theme
• This question primarily focuses on identifying gases based on their characteristic odors, which is an important aspect of chemical identification and safety awareness.

The correct answer is Double displacement reaction.

Key Points

• The given chemical reaction is K2SO4 + BaCl2 → 2KCl + BaSO4↓, where potassium sulfate reacts with barium chloride to form potassium chloride and barium sulfate.
• In this reaction, both the cations (K+ and Ba2+) and the anions (SO42− and Cl−) exchange places to form new compounds.
• The formation of an insoluble solid, barium sulfate (BaSO4), which precipitates out of the solution, signifies a double displacement reaction.
• This type of reaction is also known as a precipitation reaction because an insoluble substance (precipitate) is formed.
• Double displacement reactions usually occur in aqueous solutions and involve the exchange of ions between the reactants.

Additional Information

• Addition Reaction:
• In an addition reaction, two or more reactants combine to form a single product.
• For example, the reaction of ethene (C2H4) with hydrogen (H2) to form ethane (C2H6) is an addition reaction.
• This reaction does not involve the exchange of ions or formation of a precipitate as seen in the given question.
• Displacement Reaction:
• A displacement reaction occurs when one element displaces another in a compound.
• For example, in the reaction Zn + CuSO4 → ZnSO4 + Cu, zinc displaces copper from copper sulfate.
• The given reaction does not involve a single element replacing another; instead, ions are exchanged between compounds.
• Decomposition Reaction:
• In a decomposition reaction, a single compound breaks down into two or more simpler substances.
• For example, the decomposition of calcium carbonate (CaCO3) into calcium oxide (CaO) and carbon dioxide (CO2) is a decomposition reaction.
• The reaction in the question involves two reactants forming two products, making it a double displacement reaction, not a decomposition reaction.
• Double Displacement Reaction:
• These reactions involve the exchange of ions between two compounds to form two new compounds.
• They often result in the formation of a precipitate, a gas, or a neutral molecule like water.
• The given reaction is a classic example of a double displacement reaction, where barium sulfate precipitates out.
• Double displacement reactions play an important role in various fields, including analytical chemistry and industrial processes.