The Bihar Board Class 12 Chemistry Guess Paper 2025 is designed strictly according to the latest BSEB exam pattern. Chemistry is one of the most important subjects for Science stream students as it carries high weightage in board exams as well as in competitive exams like JEE and NEET. This model paper includes 35 objective questions, 5 short answer questions, and 3 long answer questions with solutions, which will help students in better revision and practice. Solving this paper will boost confidence, improve problem-solving ability, and make exam preparation stronger.

Bihar Board Class 12 Chemistry Guess Paper 2025

Subject: Chemistry
Maximum Marks: 70
Time: 3 Hours

Section A – Objective Questions (35 × 1 = 35 Marks)

(Each question carries 1 mark. Four options are given, choose the correct one.)

Q1. The hybridization of carbon in C₂H₂ is –
(a) sp³
(b) sp²
(c) sp
(d) sp³d
Answer: (c) sp

Q2. Which one is an example of heterogeneous catalysis?
(a) Haber process
(b) Contact process
(c) Hydrogenation of oils using Ni catalyst
(d) Hydrolysis of ester by HCl
Answer: (c) Hydrogenation of oils using Ni catalyst

Q3. Equivalent weight of an acid is –
(a) Molecular weight / Basicity
(b) Molecular weight × Basicity
(c) Atomic weight / Valency
(d) None
Answer: (a) Molecular weight / Basicity

Q4. Which gas is used in Haber’s process?
(a) CO + H₂
(b) N₂ + H₂
(c) N₂ + O₂
(d) CO₂ + H₂
Answer: (b) N₂ + H₂

Q5. Which of the following is not an alkali metal?
(a) Na
(b) K
(c) Mg
(d) Li
Answer: (c) Mg

Q6. Which law governs colligative properties?
(a) Raoult’s law
(b) Henry’s law
(c) Dalton’s law
(d) Gay Lussac’s law
Answer: (a) Raoult’s law

Q7. Which of the following is used in glass etching?
(a) HF
(b) HCl
(c) H₂SO₄
(d) HNO₃
Answer: (a) HF

Q8. Which of the following is an example of biodegradable polymer?
(a) Nylon-6
(b) Dacron
(c) PHBV
(d) Bakelite
Answer: (c) PHBV

Q9. What is the IUPAC name of CH₃–CHO?
(a) Methanal
(b) Ethanal
(c) Acetone
(d) Ethanol
Answer: (b) Ethanal

Q10. Which metal is purified by Mond’s process?
(a) Ni
(b) Al
(c) Zn
(d) Fe
Answer: (a) Ni

Q11. Which law explains osmotic pressure?
(a) Boyle’s law
(b) Van’t Hoff law
(c) Henry’s law
(d) Graham’s law
Answer: (b) Van’t Hoff law

Q12. The order of reaction is –
(a) Always integer
(b) May be fractional
(c) Always zero
(d) Cannot be determined experimentally
Answer: (b) May be fractional

Q13. Example of a strong electrolyte –
(a) Acetic acid
(b) Glucose
(c) NaOH
(d) Urea
Answer: (c) NaOH

Q14. The main ore of aluminium is –
(a) Galena
(b) Bauxite
(c) Hematite
(d) Magnetite
Answer: (b) Bauxite

Q15. Which of the following has maximum ionic character?
(a) HF
(b) HCl
(c) HBr
(d) HI
Answer: (a) HF

Q16. The monomer of Buna-S rubber is –
(a) Styrene + Butadiene
(b) Ethylene + Benzene
(c) Vinyl chloride + Butadiene
(d) Propene + Styrene
Answer: (a) Styrene + Butadiene

Q17. Which vitamin contains cobalt?
(a) Vitamin A
(b) Vitamin B₁₂
(c) Vitamin C
(d) Vitamin D
Answer: (b) Vitamin B₁₂

Q18. Which has maximum conductivity at infinite dilution?
(a) NaCl
(b) KCl
(c) HCl
(d) NH₄OH
Answer: (c) HCl

Q19. Which compound is called marsh gas?
(a) Ethane
(b) Methane
(c) Propane
(d) Ethene
Answer: (b) Methane

Q20. Which of the following is an example of electrophilic substitution?
(a) Chlorination of methane
(b) Nitration of benzene
(c) Addition of HBr to ethene
(d) Hydrolysis of ester
Answer: (b) Nitration of benzene

Q21. The most electronegative element is –
(a) O
(b) N
(c) F
(d) Cl
Answer: (c) F

Q22. Which is a liquid metal at room temperature?
(a) Hg
(b) Na
(c) Ga
(d) K
Answer: (a) Hg

Q23. Which has sp² hybridization?
(a) CH₄
(b) C₂H₄
(c) C₂H₂
(d) NH₃
Answer: (b) C₂H₄

Q24. What is the molecular formula of bleaching powder?
(a) CaCl₂
(b) CaOCl₂
(c) CaCO₃
(d) Ca(OH)₂
Answer: (b) CaOCl₂

Q25. Which is not an isotope of hydrogen?
(a) Protium
(b) Deuterium
(c) Tritium
(d) Helium
Answer: (d) Helium

Q26. Which element is known as “greenhouse gas”?
(a) O₂
(b) CO₂
(c) N₂
(d) Ar
Answer: (b) CO₂

Q27. Which of the following is an example of ionic crystal?
(a) Diamond
(b) Graphite
(c) NaCl
(d) Ice
Answer: (c) NaCl

Q28. The magnetic behaviour of O₂ is –
(a) Diamagnetic
(b) Paramagnetic
(c) Ferromagnetic
(d) Non-magnetic
Answer: (b) Paramagnetic

Q29. Which of the following is used in photography?
(a) AgBr
(b) NaCl
(c) K₂Cr₂O₇
(d) KMnO₄
Answer: (a) AgBr

Q30. The process of coating zinc on iron is called –
(a) Galvanization
(b) Electroplating
(c) Smelting
(d) Refining
Answer: (a) Galvanization

Q31. Which is a greenhouse gas but not a primary pollutant?
(a) CO₂
(b) SO₂
(c) NO₂
(d) O₃
Answer: (a) CO₂

Q32. Which element shows variable valency?
(a) Ca
(b) Fe
(c) Na
(d) K
Answer: (b) Fe

Q33. In which form glucose exists in solution?
(a) Open chain
(b) Cyclic structure
(c) Both (a) and (b)
(d) None
Answer: (c) Both (a) and (b)

Q34. The IUPAC name of CH₃–CH₂–OH is –
(a) Methanol
(b) Ethanol
(c) Propanol
(d) Butanol
Answer: (b) Ethanol

Q35. Which of the following is a non-renewable source of energy?
(a) Solar energy
(b) Wind energy
(c) Coal
(d) Hydro energy
Answer: (c) Coal

Section B – Short Answer Questions (5 × 2 = 10 Marks)

Q1. State and explain Henry’s Law with one example.
Answer: Henry’s law states that the amount of gas dissolved in a liquid is directly proportional to the pressure of the gas at constant temperature.
Example: The solubility of CO₂ increases in soft drinks when bottled under high pressure.

Q2. What is the difference between order of reaction and molecularity of reaction?
Answer:

• Order of reaction: It is the sum of powers of concentration terms in the rate law equation. It may be zero, fractional, or integer.

• Molecularity: It is the number of molecules colliding in an elementary step. It is always a whole number (1, 2, or 3).

  

Q3. Write any two differences between physisorption and chemisorption.
Answer:

1. Physisorption is due to van der Waals forces, while chemisorption is due to chemical bond formation.

2. Physisorption is reversible and weak, while chemisorption is irreversible and strong.

Q4. What is Tollen’s reagent test? Write its reaction with aldehydes.
Answer:
Tollen’s reagent is ammoniacal silver nitrate solution. It oxidizes aldehydes to acids, depositing metallic silver.
R–CHO + 2[Ag(NH₃)₂]⁺ → R–COOH + 2Ag↓ + 4NH₃

Q5. What are nucleophiles? Give two examples.
Answer: Nucleophiles are species that donate a pair of electrons to form a new covalent bond.
Examples: OH⁻, NH₃, CN⁻.

Section C – Long Answer Questions (3 × 5 = 15 Marks)

Q1. (a) Define Colligative Properties. Explain any two colligative properties with suitable examples.
(b) Why does common salt lower the freezing point of water?

Answer:
(a) Colligative properties are those properties of solutions which depend only on the number of solute particles present and not on their nature.
Examples:

1. Relative lowering of vapour pressure (RLVP):
   P0−PP0=n2n1\frac{P^0 – P}{P^0} = \frac{n_2}{n_1}P0P0−P​=n1​n2​​
   where n2n_2n2​ = moles of solute, n1n_1n1​ = moles of solvent.

2. Elevation in boiling point:
   ΔTb=Kb⋅m\Delta T_b = K_b \cdot mΔTb​=Kb​⋅m, where KbK_bKb​ = molal elevation constant, $m$ = molality.

(b) Common salt lowers the freezing point of water because it decreases the chemical potential of water, making freezing possible only at a lower temperature. This is called Freezing Point Depression.

Q2. (a) Explain the preparation of Ethyl alcohol (Ethanol) from Ethylene.
(b) Write any two physical properties and two chemical properties of ethanol.

Answer:
(a) Preparation of Ethanol from Ethylene:
Ethylene (C₂H₄) reacts with water in the presence of dilute H₂SO₄ as catalyst to give ethanol.
C₂H₄ + H₂O → C₂H₅OH

(b) Properties:

• Physical: Ethanol is a colourless liquid, miscible with water, and has a boiling point of 351 K.

• Chemical:

  1. With Na metal: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

  2. Oxidation: Ethanol gets oxidized to acetic acid with alkaline KMnO₄.

Q3. (a) What is the difference between Electrolytic Cell and Galvanic Cell?
(b) Explain the working of a Daniel Cell with neat diagram.

Answer:
(a) Differences:

• Electrolytic cell: Converts electrical energy into chemical energy, requires external supply of current.

• Galvanic cell: Converts chemical energy into electrical energy, works spontaneously.

(b) Daniel Cell:

• Consists of zinc electrode dipped in ZnSO₄ solution and copper electrode dipped in CuSO₄ solution, connected through a salt bridge.

• Reaction:
  At anode (oxidation): Zn → Zn²⁺ + 2e⁻
  At cathode (reduction): Cu²⁺ + 2e⁻ → Cu
  Overall: Zn + Cu²⁺ → Zn²⁺ + Cu

This produces electrical energy.

Bihar Board Class 12 Chemistry Guess Paper 2025

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