CBSE Class 12 Chemistry Question Paper 2025 (Set 3 - 56/2/3)

Which among the following is a false statement?

• (A) Rate of zero order reaction is independent of initial concentration of reactant.
• (B) Half-life of a zero order reaction is inversely proportional to the rate constant.
• (C) Molecularity of a reaction may be zero.
• (D) For a first order reaction, t_1/2 = 0.693/k.

The charge required for the reduction of 1 mol of MnO₄^- to MnO₂ is

• (A) 1F
• (B) 3F
• (C) 5F
• (D) 6F

The element having [Ar]3d¹⁰4s¹ electronic configuration is

• (A) Cu
• (B) Zn
• (C) Cr
• (D) Mn

The number of molecules that react with each other in an elementary reaction is a measure of the:

• (A) activation energy of the reaction
• (B) stoichiometry of the reaction
• (C) molecularity of the reaction
• (D) order of the reaction

The diamagnetic species is: [At. No. Co = 27, Fe = 26, Ni = 28]

• (A) [Ni(CN)₄]^2-
• (B) [NiCl₄]^2-
• (C) [Fe(CN)₆]^3-
• (D) [CoF₆]^3-

The complex ions [Co(NH₃)₅(NO₂)]²⁺ and [Co(NH₃)₅(ONO)]²⁺ are called

• (A) Ionization isomers
• (B) Linkage isomers
• (C) Co-ordination isomers
• (D) Geometrical isomers

What will be formed after oxidation reaction of secondary alcohol with chromic anhydride (CrO₃)?

• (A) Aldehyde
• (B) Ketone
• (C) Carboxylic acid
• (D) Ester

Which is the correct IUPAC name for
 

• (A) Methylchlorobenzene
  
• (B) Toluene
  
• (C) 1-Chloro-4-Methylbenzene
  
• (D) 1-Methyl-4-Chlorobenzene

Which of the following is/are examples of denaturation of protein?

• (A) Coagulation of egg white
• (B) Curdling of milk
• (C) Clotting of blood
• (D) Both (A) and (B)

The conversion of phenol to salicylic acid can be accomplished by

• (A) Reimer-Tiemann reaction
• (B) Friedel-Crafts reaction
• (C) Kolbe reaction
• (D) Coupling reaction

Scurvy is caused due to deficiency of

• (A) Vitamin B1
• (B) Vitamin B2
• (C) Ascorbic acid
• (D) Glutamic acid

Nucleotides are joined together by

• (A) Glycosidic linkage
• (B) Peptide linkage
• (C) Hydrogen bonding
• (D) Phosphodiester linkage

Assertion (A): Cu cannot liberate H₂ on reaction with dilute mineral acids.

Reason (R): Cu has positive electrode potential.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): In a first order reaction, if the concentration of the reactant is doubled, its half-life is also doubled.

Reason (R): The half-life of a reaction does not depend upon the initial concentration of the reactant in a first order reaction.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): Vitamin D cannot be stored in our body.

Reason (R): Vitamin D is fat soluble vitamin and is not excreted from the body in urine.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis.

Reason (R): Aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Name the following coordination compounds according to IUPAC norms:

(a) [Co(NH₃)₄(H₂O)Cl]Cl₂

(b) [CrCl₂(en)₂]Cl

What is meant by the Rate law and Rate constant of a reaction. Identify the order of a reaction if the units of its Rate constant are :

(a) \( \mathrm{s^{-1}} \)

(b) \( \mathrm{mol^{-1}\ L\ s^{-1}} \)

Complete and balance the following chemical equations :
(a) \(\mathrm{8MnO_4^- + 3S_2O_3^{2-} + H_2O \longrightarrow}\)
(b) \(\mathrm{Cr_2O_7^{2-} + 3Sn^{2+} + 14H^+ \longrightarrow}\)

The rate constant for a zero order reaction A → P is 0.0030 mol L^-1s^-1. How long will it take for the initial concentration of A to fall from 0.10 M to 0.075 M?

The decomposition of NH₃ on platinum surface is zero order reaction. What are the rates of production of N₂ and H₂ if k = 2.5 × 10^-4 mol L^-1 s^-1?

Give reasons for the following observations :

(a) p-Chloronitrobenzene reacts with (aq) NaOH at 443 K to give p-nitrophenol whereas chlorobenzene reacts with the same reagent at 623 K and 300 atm.

(b) Main product obtained when chloroethane reacts with KCN is propane nitrile while with AgCN it is ethyl isocyanide.

Henry's law constant for \(\mathrm{CO_2}\) in water is \(1.67 \times 10^{8}\) Pa at 298 K. Calculate the number of moles of \(\mathrm{CO_2}\) in 540 g of soda water when packed under \(3.34 \times 10^{5}\) Pa at the same temperature.

Give reasons:

(a) Fuel cells are preferred for production of electrical energy than thermal plants.

(b) Iron does not rust even if zinc coating is broken in a galvanized pipe.

(c) In the experimental determination of electrolytic conductance, Direct Current (DC) is not used.

(a) \(E^{\circ}_{(\mathrm{Mn^{2+}/Mn})}\) is \(-1.18\ \mathrm{V}\). Why is this value highly negative in comparison to neighbouring d-block elements?

(b) What is lanthanoid contraction?

(c) Zn, Cd and Hg are soft metals. Why?

Using valence bond theory, explain the hybridization and magnetic character of the following:
(a) \([\mathrm{Co(NH_3)_6}]^{3+}\)
(b) \([\mathrm{Ni(CO)_4}]\)
[At. no. : Co = 27, Ni = 28]

Write the electronic configuration of d⁵ ion when Δ_o > P.

Define the following:

(i) Enantiomers

(ii) Racemic mixture

Why is chlorobenzene resistant to nucleophilic substitution reaction?

Explain the following reactions and write chemical equation involved:

Wolff-Kishner reduction

Explain the following reactions and write chemical equation involved:

Etard reaction

Explain the following reactions and write chemical equation involved:

Cannizzaro reaction

(B) Write the structures of A, B and C in the following sequence of reactions:

(a) \( \text{CH}_3\text{COOH} \xrightarrow{\text{SOCl}_2} A \xrightarrow{\text{H}_2,\ \text{Pd-BaSO}_4} B \xrightarrow{\text{H}_2\text{N-NH}_2} C \)

(b) \( \text{CH}_3\text{CN} \xrightarrow[\text{2. H}_2\text{O}]{\text{1. DIBAL-H}} A \xrightarrow{\text{Dil. NaOH}} B \xrightarrow{\Delta} C \)

Define the following terms :
(a) Native protein
(b) Nucleotide
(c) Essential amino acid

Read the passage and answer: The spontaneous flow of the solvent through a semipermeable membrane from a pure solvent to a solution or from a dilute solution to a concentrated solution is called osmosis. The phenomenon of osmosis can be demonstrated by taking two eggs of the same size. In an egg, the membrane below the shell and around the egg material is semipermeable. The outer hard shell can be removed by putting the egg in dilute hydrochloric acid. After removing the hard shell, one egg is placed in distilled water and the other in a saturated salt solution. After some time, the egg placed in distilled water swells-up while the egg placed in salt solution shrinks. The external pressure applied to stop the osmosis is termed as osmotic pressure (a colligative property). Reverse osmosis takes place when the applied external pressure becomes larger than the osmotic pressure.

(a) Define reverse osmosis. Name one SPM which can be used in the process of reverse osmosis.

What do you expect to happen when red blood corpuscles (RBC's) are placed in 0.5% NaCl solution?

Which one of the following will have higher osmotic pressure in 1M KCl or 1M urea solution. Justify your answer.

Why osmotic pressure is a colligative property?

Amines have a lone pair of electrons on nitrogen atom due to which they behave as Lewis base. Greater the value of \( K_b \) or smaller the value of \( pK_b \), stronger is the base. Amines are more basic than alcohols, ethers, esters, etc. The basic character of aliphatic amines should increase with the increase of alkyl substitution. But it does not occur in a regular manner as a secondary aliphatic amine is unexpectedly more basic than a tertiary amine in aqueous solutions. Aromatic amines are weaker bases than ammonia and aliphatic amines. Electron releasing groups such as \( -CH_3 \), \( -OCH_3 \), \( -NH_2 \), etc., increase the basicity while electron-withdrawing substituents such as \( -NO_2 \), \( -CN \), halogens etc., decrease the basicity of amines. The effect of these substitute is more at p\( ^- \) than at m\( ^- \) position.

(a) Arrange the following in the increasing order of their basic character. Give reason: 

Why pK_b of aniline is more than that of methylamine?

Arrange the following in the increasing order of their basicity in an aqueous solution:
\(\text{(CH}_3\text{)}_3\text{N}, \ \text{(CH}_3\text{)}_2\text{NH}, \ \text{NH}_3, \ \text{CH}_3\text{NH}_2\)

Why ammonolysis of alkyl halides is not a good method to prepare pure amines?

Calculate the standard Gibbs energy (\( \Delta G^\circ \)) of the following reaction at 25°C: \[ \text{Au}(s) + \text{Ca}^{2+}(1M) \to \text{Au}^{3+}(1M) + \text{Ca}(s) \] \[ E^\circ_{\text{Au}^{3+}/\text{Au}} = +1.5 \, \text{V}, \quad E^\circ_{\text{Ca}^{2+}/\text{Ca}} = -2.87 \, \text{V} \] Predict whether the reaction will be spontaneous or not at 25°C. [1 F = 96500 C mol\(^{-1}\)]

Tarnished silver contains \( Ag_2S \). Can this tarnish be removed by placing tarnished silverware in an aluminium pan containing an inert electrolytic solution such as NaCl? The standard electrode potential for the half reaction: \[ \text{Ag}_2\text{S}(s) + 2e^- \to 2\text{Ag}(s) + S^{2-}(aq) \, (\text{E}^\circ = -0.71 \, \text{V}) \] \[ \text{Al}^{3+}(aq) + 3e^- \to \text{Al}(s) \, (\text{E}^\circ = -1.66 \, \text{V}) \]

Define the following:

(i) Cell potential

(ii) Fuel cell

Calculate the emf of the following cell at 25°C: 
\[ \text{Zn(s)} | \text{Zn}^{2+}(0.1M) || \text{Cd}^{2+}(0.01M) | \text{Cd(s)} \] Given: \[ E^\circ_{\text{Cd}^{2+}/\text{Cd}} = -0.40 \, V, \, E^\circ_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, V \] \[ [\log 10 = 1] \]

An organic compound 'A', molecular formula C₂H₆O oxidises with CrO₃ to form a compound 'B'. Compound 'B' on warming with iodine and aqueous solution of NaOH gives a yellow precipitate of compound 'C'. When compound 'A' is heated with conc. H₂SO₄ at 413 K gives a compound 'D', which on reaction with excess HI gives compound 'E'. Identify compounds 'A', 'B', 'C', 'D' and 'E' and write chemical equations involved.

(B) (a) Write chemical equations of the following reactions:

(i) Phenol is treated with conc. HNO₃

(ii) Propene is treated with B₂H₆ followed by oxidation by H₂O₂/OH^-.

(iii) Sodium t-butoxide is treated with CH₃Cl.

(b) Give a simple chemical test to distinguish between butan-1-ol and butan-2-ol.

(c) Arrange the following in increasing order of acid strength:

phenol, ethanol, water

Give IUPAC name of CH₃-CH=CH-CHO.

Give a simple chemical test to distinguish between propanal and propanone.

How will you convert the following:

(i) Toluene to benzoic acid

(ii) Ethanol to propan-2-ol

(iii) Propanal to 2-hydroxy propanoic acid

Complete each synthesis by giving missing starting material, reagent or products: