CBSE Class 12 Chemistry Question Paper 2025 with Solutions Set 2 ( Available)- Download PDF

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.

• (1) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (2) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (3) Assertion (A) is true, but Reason (R) is false.
• (4) 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.

• (1) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (2) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (3) Assertion (A) is true, but Reason (R) is false.
• (4) Assertion (A) is false, but Reason (R) is true.

Assertion (A): Cu cannot liberate \( H_2 \) on reaction with dilute mineral acids.
Reason (R): Cu has positive electrode potential.

• (1) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (2) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (3) Assertion (A) is true, but Reason (R) is false.
• (4) 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.

• (1) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• (2) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• (3) Assertion (A) is true, but Reason (R) is false.
• (4) Assertion (A) is false, but Reason (R) is true.

Scurvy is caused due to deficiency of

• (1) Vitamin B1
• (2) Vitamin B2
• (3) Ascorbic acid
• (4) Glutamic acid

Nucleotides are joined together by

• (1) Glycosidic linkage
• (2) Peptide linkage
• (3) Hydrogen bonding
• (4) Phosphodiester linkage

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

• (1) Coagulation of egg white
• (2) Curdling of milk
• (3) Clotting of blood
• (4) Both (1) and (2)

The conversion of phenol to salicylic acid can be accomplished by

• (1) Reimer-Tiemann reaction
• (2) Friedel-Crafts reaction
• (3) Kolbe reaction
• (4) Coupling reaction

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

• (1) Aldehyde
• (2) Ketone
• (3) Carboxylic acid
• (4) Ester

Which is the correct IUPAC name for

• (1) Methylchlorobenzene
• (2) Toluene
• (3) 1-Chloro-4-Methylbenzene
• (4) 1-Methyl-4-Chlorobenzene

The diamagnetic species is :

At. No. Co = 27, Fe =26, Ni= 28]

• (1) \( [Ni(CN)_4]^{2-} \)
• (2) \( [NiCl_4]^{2-} \)
• (3) \( [Fe(CN)_6]^{3-} \)
• (4) \( [CoF_6]^{3-} \)

The complex ions \([Co(NH_3)_5(NO_2)]^{2+}\) and \([Co(NH_3)_5(ONO)]^{2+}\) are called

• (1) Ionization isomers
• (2) Linkage isomers
• (3) Co-ordination isomers
• (4) Geometrical isomers

The element having \([Ar]3d^{10}4s^1\) electronic configuration is

• (1) Cu
• (2) Zn
• (3) Cr
• (4) Mn

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

• (1) activation energy of the reaction
• (2) stoichiometry of the reaction
• (3) molecularity of the reaction
• (4) order of the reaction

Which among the following is a false statement?

• (1) Rate of zero order reaction is independent of initial concentration of reactant.
• (2) Half-life of a zero order reaction is inversely proportional to the rate constant.
• (3) Molecularity of a reaction may be zero.
• (4) For a first order reaction, \( t_{1/2} = 0.693/k \).

The charge required for the reduction of 1 mol of \( MnO_4^- \) to \( MnO_2 \) is

• (1) 1 F
• (2) 3 F
• (3) 5 F
• (4) 6 F

(a) In the following pair of halogen compounds, which compound undergoes \( S_N1 \) reaction faster and why?


 

(b) Arrange the following compounds in increasing order of their reactivity towards \( S_N2 \) displacement: 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane.

A reaction is of second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is (i) doubled, (ii) reduced to half?

When \( FeCr_2O_4 \) is fused with \( Na_2CO_3 \) in the presence of air, it gives a yellow solution of compound (A). Compound (A) on acidification gives compound (B). Compound (B) on reaction with KCl forms an orange-colored compound (C). An acidified solution of compound (C) oxidizes \( Na_2SO_3 \) to (D). Identify (A), (B), (C), and (D).

Explain \( [Co(NH_3)_6]^{3+} \) is an inner orbital complex whereas \( [Ni(NH_3)_6]^{2+} \) is an outer orbital complex. [At. No. Co = 27, Ni = 28]

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

(B) The decomposition of \( NH_3 \) on a platinum surface is a zero-order reaction. What are the rates of production of \( N_2 \) and \( H_2 \) if \( k = 2.5 \times 10^{-4} \, mol L^{-1} \, s^{-1} \)?

A solution containing 15 g urea (molar mass = 60 g mol\(^{-1}\)) per litre of solution in water has the same osmotic pressure (isotonic) as a solution of glucose (molar mass = 180 g mol\(^{-1}\)) in water. Calculate the mass of glucose present in one litre of its solution.

Calculate \( \Lambda_m^0 \) for acetic acid and its degree of dissociation (\( \alpha \)) if its molar conductivity is 48.1 \( \Omega^{-1} \, cm^2 \, mol^{-1} \).

Given that
\( \Lambda_m^0 (HC) = 426 \, \Omega^{-1} \, cm^2 \, mol^{-1} \),
\( \Lambda_m^0 (NaCl) = 126 \, \Omega^{-1} \, cm^2 \, mol^{-1} \),
\( \Lambda_m^0 (CH_3COONa) = 91 \, \Omega^{-1} \, cm^2 \, mol^{-1} \).

(a) Why is \( Cr^{2+} \) strongly reducing while \( Mn^{3+} \) is strongly oxidizing?

(b) Write two consequences of lanthanide contraction.

(c) Which element of the 3d series has the lowest enthalpy of atomisation and why?

Write IUPAC names of the following coordination entities:

(a) \( [Fe(en)_2Cl_2]^+ \)

(b) \( [Co(NH_3)_4(H_2O)Br]SO_4 \)

(c) \( [Ni(CN)_4]^{2-} \)

(A) Explain the following reactions and write chemical equations involved:

(a) Wolff-Kishner reduction

(b) Etard reaction

(c) Cannizzaro reaction

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

(a) Define the following:

(i) Enantiomers

(ii) Racemic mixture

(b) Why is chlorobenzene resistant to nucleophilic substitution reactions?

(a) Write the product obtained when D-glucose reacts with \( H_2N - OH \).

(b) Amino acids show amphoteric behaviour, why?

(c) Why can't vitamin C be stored in our body?

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 \(–CH_3\), \(–NH_2\), etc., increase the basicity while electron-withdrawing substituents such as \(–NO_2\), –CN, halogens, etc., decrease the basicity of amines. The effect of these substituents is more at the p₊ than at m₋ position.

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

(b) Why pKₐ of aniline is more than that of methylamine?

(c) (i) Arrange the following in the increasing order of their basic character in an aqueous solution:

(c) (ii) Why ammonolysis of alkyl halides is not a good method to prepare pure amines?

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.

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

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

(c) Why osmotic pressure is a colligative property?

(A) An organic compound \( A \), molecular formula \( C_2H_6O \), oxidises with \( Cr_2O_7 \) 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. \( H_2SO_4 \) at 413 K, it 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) OR Write chemical equations of the following reactions:
(i) Phenol is treated with conc. \( HNO_3 \).

(ii) Propene is treated with \( B_2H_6 \) followed by oxidation by \( H_2O_2 / OH^- \).

(iii) Sodium t-butoxide is treated with \( CH_3Cl \).

(B) (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.

(A) (a) Give IUPAC name of \( CH_3 = CH - CH = CH - CHO \).

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

(c) How will you convert the following:

(i) Toluene to benzoic acid.

(ii) Ethanol to propan-2-ol.

(iii) Propanal to 2-hydroxy propanoic acid.

(B) OR Complete each synthesis by giving missing starting material, reagent, or products:

(A) (a) Calculate the standard Gibbs energy (\( \Delta G^\circ \)) of the following reaction at 25°C:
\[ Au(s) + Ca^{2+}(1M) \to Au^{3+}(1M) + Ca(s) \]
\[ E^\circ_{Au^{3+}/Au} = +1.5 \, V, \quad E^\circ_{Ca^{2+}/Ca} = -2.87 \, V \]

Predict whether the reaction will be spontaneous or not at 25°C.
[1 F = 96500 C mol\(^{-1}\)]

(b) 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: \[ Ag_2S(s) + 2e^- \to 2Ag(s) + S^{2-}(aq) \, (E^\circ = -0.71 \, V) \] \[ Al^{3+}(aq) + 3e^- \to Al(s) \, (E^\circ = -1.66 \, V) \]

(B) (a) (i) OR Define the following:

(i) Cell potential

(a) (ii) Fuel cell

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