Term and conditions

NIOS On Demand Exam 2025 Section A: Multiple Choice Questions (Questions 1-16) 1. The linear molecule with net dipole moment zero: Answer: (B) CO₂ 2. Colligative property for determining molar mass of proteins: Answer: (B) Osmotic pressure 3. Extensive property: Answer: (D) Volume Or, Bond dissociation enthalpy applicable only for: Answer: (A) Gaseous molecules 4. Conjugate acid of: Answer: (C) Or, Highest pH value: Answer: (B) 1 M NaOH 5. H–O–H bond angle in water: Answer: (D) 104.5° Or, Thermal stability order of alkaline earth metal carbonates: Answer: (D) 6. Property not exhibited by: Answer: (B) Oxidizing properties Or, Gas preventing metal oxidation during welding: Answer: (A) Hydrogen 7. Lanthanoids and actinoids resemblance: Answer: (B) Prominent oxidation state Or, Colourless ion aqueous solution: Answer: (D) 8. Temporary electron displacement in molecules with multiple bonds: Answer: (B) Electromeric effect 9. Solution discharging bromine colour: Answer: (C) Both alkenes and alkynes Or, Sulphonation of benzene reagent: Answer: (B) Concentrated H₂SO₄ 10. Higher melting/boiling points of haloalkanes: Answer: (C) Intermolecular dipole-dipole interaction 11. Product of phenol with CHCl₃ and NaOH: Answer: (B) Salicylaldehyde Or, Enzyme converting glucose to ethanol: Answer: (D) Zymase 12. Hemiacetals are chemically: Answer: (A) Alkoxy alcohols 13. Compound forming stable diazonium salt at 273–278 K: Answer: (B) Aniline Or, Sulphonation of aniline at 455–475 K: Answer: (D) Sulphanilic acid 14. Chemically, enzymes are: Answer: (D) Globular proteins 15. Polymer softens on heating, rigid on cooling: Answer: (D) Thermoplastic 16. 100% biodegradable washing material with carboxylate ion: Answer: (A) Soap Section A: Objective Type Questions (Questions 17–28) Question 17: Fill in the blanks. (a) 58.5 g/mol is the molar mass of NaCl. (b) A mole is the amount of substance containing entities as in 12 g of C-12 isotope. (c) 1 mm = 0.001 m. (d) Molecular formula is always an integral multiple of the empirical formula. Question 18: Answer based on the VSEPR theory. (Attempt any two) (a) The electron pairs arrange to minimize their mutual repulsion. (b) The bond angle of a molecule is linked to mutual repulsion. (c) For five electron pairs, the geometry is trigonal bipyramidal. Question 19: Write True (T) or False (F) for the statements. (Attempt any two) (a) Benzene-chloroform mixture exhibits positive deviation from Raoult’s law: T (b) Boiling point is a colligative property: T (d) Two liquids are miscible when they dissolve in each other in all proportions: T Question 20: Write True (T) or False (F). (Attempt any two) (a) Electrons flow from cathode to anode in a galvanic cell: F (b) Salt bridge connects two half-cells without mixing electrolytes: T (d) Conductivity = conductance × cell constant: T Question 21: Write True (T) or False (F). (Attempt any two) (a) Reaction of lithium with water is less vigorous than sodium: T (c) Calcium imparts brick-red colour to flame: T (d) Chlorophyll is a complex compound of magnesium: T Question 22: Write True (T) or False (F). (Attempt any two) (a) Sulphur shows two, four, and six valencies in compounds: T (b) Fluorine is prepared by electrolysis of hydrogen fluoride: T (d) Oxidation state of chlorine in chlorous acid is +1: T Question 23: Write True (T) or False (F). (Attempt any two) (a) TiO₂ compounds are white and diamagnetic, TiCl₄ compounds are coloured and paramagnetic: T (c) Scandium does not exhibit variable oxidation states: T (d) Among Al, Zn, Mg, Fe, the densest element is Fe: T Question 24: Coordination compounds. (Attempt any two) (a) [Co(CN)₆]³⁻ is stronger due to stronger ligand field compared to [CoF₆]³⁻. (b) To distinguish [Co(NH₃)₅Br]SO₄ and [Co(NH₃)₅SO₄]Br, use AgNO₃ to precipitate bromide ions. (d) The bidentate ligand in [Co(en)₃]³⁺ is ethylenediamine (en). 25. Chemical properties of benzene (Attempt any two): (a) Electrophilic substitution reactions, e.g., nitration. (b) Reacts with chlorine in sunlight to form benzene hexachloride. (c) Hydrogenation in the presence of nickel catalyst forms cyclohexane. 26. Characteristics of nucleophiles (Attempt any two): (a) Electron-rich species. (b) Attacks electron-deficient centers. (c) Example: OH⁻. 27. Match the following (Attempt any two): (a) Phenol – Antiseptic. (b) Ethanol – Solvent. (c) Formalin – Preservative. 28. Characteristics of polymers (Attempt any two): (a) Polyethylene – Thermoplastic. (b) Bakelite – Thermosetting. (c) Natural rubber – Elasticity. Section B: Short Answer Questions (Questions 29–38) 29. Explain the structure of the atom in brief: Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in orbitals. 30. State Boyle’s law and its mathematical expression: Boyle's law states that the pressure of a gas is inversely proportional to its volume at constant temperature. Mathematically, P₁V₁ = P₂V₂. 31. Write any two characteristics of a chemical reaction: (a) Formation of a precipitate. (b) Evolution of gas. 32. Define molarity and molality: (a) Molarity: Number of moles of solute per litre of solution. (b) Molality: Number of moles of solute per kilogram of solvent. 33. Explain the electrochemical series: The electrochemical series ranks elements and ions by their standard electrode potentials, indicating their tendency to gain or lose electrons. 34. Write two uses of heavy water: (a) Moderator in nuclear reactors. (b) Tracer in chemical and biological research. 35. Describe one method of nitrogen preparation: Fractional distillation of liquid air separates nitrogen from oxygen and argon. 36. Explain the octet rule with an example: Atoms tend to have eight electrons in their valence shell for stability. Example: NaCl, where Na loses one electron, and Cl gains one. 37. Describe the term 'isomerism': Isomerism is the existence of compounds with the same molecular formula but different structural arrangements, e.g., ethanol and dimethyl ether. 38. Write any two physical properties of metals: (a) High thermal and electrical conductivity. (b) Malleable and ductile. Section C: Long Answer Questions (Questions 39–43) 39. Explain the periodic table’s classification in detail: The periodic table is divided into groups (vertical columns) and periods (horizontal rows) based on atomic number. Elements are classified as metals, nonmetals, and metalloids. 40. Describe the process of fractional distillation with an example: Fractional distillation separates mixtures into components based on boiling points. Example: Crude oil refining into gasoline, diesel, etc. 41. Explain the greenhouse effect and its consequences: The greenhouse effect is the trapping of heat by greenhouse gases like CO₂, causing global warming, melting polar ice caps, and rising sea levels. 42. Write a detailed note on covalent bonding: Covalent bonding involves the sharing of electron pairs between atoms, forming molecules with strong bonds. Example: H₂O, where hydrogen and oxygen share electrons. 43. Explain the role of enzymes in biological reactions: Enzymes act as biological catalysts, speeding up chemical reactions by lowering activation energy without being consumed, e.g., amylase breaks down starch into sugars.

NIOS Chemistry Solved Sample Paper for On-Demand Exam 2025

NIOS On-Demand Exam 2025: Download Solved Chemistry Question Paper PDF for Guaranteed Success

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nios class 12 English tma 2025

Nios class 12 English tma Solved 2024-25