BSEB 12 Chemistry Answer Key 2025

Bihar Board 12th Chemistry Answer Key 2025

Bihar Board 12th Chemistry Answer Key 2025

>Bihar Board (BSEB) 12th Chemistry Solved Paper 2025

Section A: Objective/Single Choice Type Questions

Total Marks: 35
Total Number of Questions: 70
Number of Questions to be Answered: 35

If more than 35 questions are answered, only the first 35 will be evaluated for marking.
Each question of this section carries 1 mark



Bihar Board 12th Chemistry Paper 2025 Answer Key, SET-A

1 - A15 - D29 - A43 - C57 - C
2 - C16 - B30 - A44 - A58 - C
3 - D17 - B31 - D45 - D59 - A
4 - A18 - C32 - A46 - D60 - C
5 - A19 - A33 - B47 - A61 - A
6 - B20 - A34 - B48 - B62 - A
7 - D21 - B35 - A49 - B63 - D
8 - B22 - A36 - B50 - C64 - D
9 - C23 - B37 - C51 - D65 - D
10 - D24 - B38 - B52 - B66 - A
11 - A25 - B39 - C53 - C67 - C
12 - B26 - B40 - C54 - D68 - C
13 - C27 - C41 - A55 - A69 - A
14 - A28 - D42 - B56 - A70 - C


Section-B: Short Answer Type Questions

Total Marks: 20
Total Number of Question: 20
Number of Questions to be Answered: 10

If more than 10 questions are answered, only the first 10 will be evaluated for marking.
Each question of this section carries 2 mark


1. Distinguish between alcohol and phenol.

Alcohols and phenols both have the same functional group (OH) but OH is attached to aliphatic carbon in alcohols while in phenol, it is attached to aromatic ring. Phenol gives ferric chloride test but alcohols does not. Phenol is more acidic than alcohols.

2. Why nitrogen molecule is less reactive?

The bond dissociation energy of the nitrogen triple bond (N≡N) is very high (about 941 kJ/mol), making it difficult for reactions to occur without sufficient activation energy. That's why nitrogen molecule is less reactive.

3. What are essential amino acids?

Essential amino acids are those that the human body cannot synthesize on its own accord, so they must be obtained through diet. There are nine essential amino acids, they are-
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine

4. O3 behaves as a strong oxidizing agent, explain.

Ozone acts as a strong oxidizing agent due to its ability to easily decompose, releasing atomic oxygen (O), which is highly reactive and acts as a strong oxidizing agent.
O3 → O2 + O


5. What do you understand by elevation in boiling point?

The phenomenon where the boiling point of a liquid increases when a non-volatile solute is added to it because, the solution has more dissolved particles than the pure solvent. Suppose Tb is the boiling point of solvent, and T is that of the solution. Thus, the disparity in the boiling points (ΔT) is known as the elevation in boiling point. This is a colligative property.

6. What happens when n-butyl chloride reacts with alcoholic KOH?

When n-butyl chloride reacts with alcoholic KOH, but-2-ene is formed as major product.
CH3–CH2–CH2–CH2–Cl → CH3–CH2–CH=CH2 + CH3–CH=CH–CH3

7. Why is ethyl alcohol not dried by anhydrous CaCl2?

Ethyl alcohol is not dried by anhydrous calcium chloride because calcium chloride forms a complex with ethanol. Instead of just absorbing the water, CaCl2 also binds to the ethanol molecules, making it ineffective as a drying agent for ethanol. This binding reduces the overall efficiency of calcium chloride in removing water from the ethanol.

8. Write Arrhenius equation.

K = A.e−Ea/RT is the Arrhenius equation that describes the temperature dependence of the rate constant of a chemical reaction.
In the equation, K is the rate constant, A is the pre-exponential factor (also known as the frequency factor), Ea is the activation energy, R is the universal gas constant and T is the temperature in Kelvin.


9. What is metamerism?

Metamerism is a type of isomerism in which compounds have the same molecular formula but differ in the arrangement of alkyl groups around a functional group (such as an ether, amine, or ketone). In metamerism, the carbon chain length on either side of the functional group is uneven.
C2H5–O–C2H5 and CH3–O–C3H7 are metamers of each other.

10. What are chiral and achiral compounds?

Compounds in which carbon is bonded to four different atoms or group of atoms and is not superimposable on its mirror image are known as chiral compounds while achiral compounds does not bonded to four different atoms or group of atoms and is superimposable on its mirror image are known as achiral compounds.

11. Write faraday's second law of electrolysis.

If the same amount of electric charge is passed through different electrolytes, the mass of the substances liberated or deposited at the electrodes is proportional to their chemical equivalent weights. This statement establish a relationship between the quantity of electricity and the amount of substance produced during electrolysis.

12. Write the IUPAC name of complex compound K3[Cr(C2O4)3].

The IUPAC name of the given complex compound is potassium trioxalatocromate(III).


13. Why PCl5 is a known compound but NCl3 is not?

Actually, both PCl5 and NCl3 are known compounds, but they differ in their stability and properties.

PCl5 exists as a known compound because phosphorus has vacant d-orbitals in its valence shell, allowing it to expand its octet and form five bonds with chlorine atoms. Nitrogen forms NCl3, but it is much less stable and more explosive than PCl5.

14. Why are alcohols more soluble in water than alkanes of same molecular weight?

Alcohols are more soluble in water than alkanes of the same molecular weight due to the presence of the hydroxyl group (-OH) in alcohols which forms hydrogen bonds with water, but this is not possible in alkanes due to absence of hydroxyl group (-OH). That's why alcohols are more soluble in water than alkanes of same molecular weight

15. Write the name of the catalyst used in Contact process and Ostwald process.

In Contact process, V2O5 catalyst is used.
In Ostwald process, platinum or platinum-rhodium alloy is used as a catalyst.

16. Write the formula of Tetraaminaquachlorido cobalt(III)chloride.

The formula for Tetraammineaquachloridocobalt(III) chloride is [Co(NH3)4(H2O)Cl]Cl2]


17. How would you prepare ethane from methyl iodide?

Ethane can easily be prepared from methyl iodide by Wurtz reaction in which two molecules of methyl iodide reacts with sodium metal in the presence of dry ether.
2 CH3I + Na → C2H6 + 2NaI

18. How would you prepare iodiform from acetylene?

Acetylene is first converted to acetaldehyde via hydration and then reacts with iodine in NaOH to yield iodoform.
CH≡CH + H2O ---Hg+2/H+ → CH3CHO
CH3CHO + 3I2 + 4NaOH → CHI3 + HCOONa + 3NaI + 2H2

19. What is slag?

Slag is a byproduct formed during the smelting or refining of metal ores. It is a mixture of oxides, silicates, and other compounds. Slag is produced when impurities in the ore combine with fluxes (such as limestone) added during the smelting process.

20. What are macromolecules?

Macromolecules are very large molecules that are formed by the polymerization of smaller molecules called monomers. Synthetic fibres, carbohydrates, proteins, lipids etc are examples of macromolecules.


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