CBSE Class 12 PCM Chemistry Board Paper 2026 — Set 4

Oxidation of chloroform by air in the presence of sunlight produces a poisonous gas known as :

Lucas reagent produces cloudiness immediately with :

Which of the following d-orbitals experience more repulsion in the crystal field splitting of octahedral complex ?

The chelating ligand used for the treatment of lead poisoning is :

The correct order of decreasing basicities of C₂H₅NH₂, (C₂H₅)₂NH and (C₂H₅)₃N in aqueous solution is :

The boiling point of one molal NaCl solution, assuming NaCl to be completely dissociated in water is : (K_b for water = 0·52 K kg mol⁻¹)

When a liquid and its vapour are at equilibrium and the pressure is suddenly decreased :

Nucleic acids are polymers of :

The rate of a first order reaction is 5·6 × 10⁻⁴ mol L⁻¹ s⁻¹, when the concentration of reactant is 0·2 mol L⁻¹ The rate constant ‘k’ is :

In the reaction of NaOBr with amide, the carbonyl carbon is lost as :

Assertion (A) : Diazonium salts of aromatic amines are more stable than those of aliphatic amines. Reason (R) : Diazonium salts of aliphatic amines undergo resonance.

Assertion (A) : For complex reaction, order of reaction is given by the slowest step. Reason (R) : Order of a reaction is an experimental quantity.

Assertion (A) : E ° _Sc³⁺ / Sc²⁺ E has low value. Reason (R) : Because of the stability of Sc³⁺ ion which has a noble gas configuration.

(a) Reactions of which order will show the rate to be independent of the concentration of the reactant ? Give one example of this order.

(b) State the condition under which a bimolecular reaction may be kinetically a first order reaction.

(a) Explain the following with the help of Henry’s law :

(i) Bends

(ii) Anoxia

How does sprinkling of salt help in clearing the snow covered roads in hilly areas ? Write the name of the colligative property involved in this process.

Write IUPAC names of the following compounds :

(a) [Cr(NH₃)₄ (ONO)Cl] NO₃

(b) Na[Ag(CN)₂]

What are the hydrolysis products of the following ?

(a) Lactose

(b) DNA containing Thymine

Draw the structures of major product(s) in each of the following reactions :

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

What happens when :

(a) Propanenitrile is treated with phenyl magnesium bromide followed by hydrolysis ?

(b) p-fluorotoluene is treated with CrO₃ in the presence of acetic anhydride followed by hydrolysis with aqueous acid.

(c) Phthalic acid is treated with NH₃ followed by heating ?

Write chemical reactions in support of your answer.

Answer the following questions :

(a) Why is direct current (DC) not used to measure the resistance of an ionic solution ?

(b) Why are the products of electrolysis different for the electrolysis of aqueous solution of AgNO₃ with silver electrodes and electrolysis of aqueous solution of AgNO₃ with platinum electrodes ?

(c) Why are magnesium blocks fixed to the iron pipelines carrying water ?

When a coordination compound CoCl₃ . 6NH₃ is mixed with excess of AgNO₃ solution, 3 moles of AgCl are precipitated per mole of the compound. Write the structural formula of the complex, IUPAC name, its hybridisation and magnetic behaviour on the basis of valence bond theory.

(i) How many geometrical isomers are possible in each of the following complexes ?

(I) [Cr(C₂O)₃]³⁻

(II) [Co(NH₃)₃Cl₃]

(ii) [Co(NH₃)₆]³⁺ is an inner orbital complex whereas [Ni(NH₃)₆]²⁺ is an outer orbital complex. Why ?

[Atomic number : Co = 27, Ni = 28]

(iii) Write the formula of Wilkinson catalyst and its use.

Calculate the vapour pressure of a solution containing 61 g of benzoic acid (molar mass = 122 g mol⁻¹) dissolved in 500 g of benzene when the vapour pressure of pure benzene at this temperature of experiment is 66 torr. Assume complete dimerization of benzoic acid in benzene.

Consider the decomposition of hydrogen peroxide (H₂O₂) as per the equation given below :

2H₂O₂ ⎯⎯ I⁻/Alkaline Medium⎯→ 2H₂O + O₂

The mechanism for this reaction was found to be :

Step I : H₂O₂ + I⁻ → H₂O + IO⁻ (slow)

Step II : H₂O₂ + IO⁻ → H₂O + I⁻ + O2 (fast)

(a) Write the rate law expression.

(b) Determine the order of reaction with respect to H₂O₂, I⁻ and overall order of reaction.

(c) What is the molecularity of the reaction in Step II ?

Answer the following :

(a) Which isomer of C₄H₉Br is most reactive towards S_N1 reaction ?

(b) Predict the alkene that would be formed by dehydrohalogenation of 1-Bromo-1-methylcyclohexane.

(c) Although chlorine shows strong – I effect, yet it is ortho- and para-directing in electrophilic aromatic substitution reactions. Why

(i) Account for the following :

(I) MnO is basic while Mn₂O₇ is acidic.

(II) Iron has higher enthalpy of atomization than that of copper.

(III) Mn³⁺ is a stronger oxidising agent than Cr³⁺.

(ii) How do you prepare potassium dichromate from sodium chromate ? Write balanced chemical equation for each step.

Answer the following questions :

(i) Why is chemistry of actinoids more complicated as compared to lanthanoids ?

(ii) E°_M²⁺/M values are not regular for first row transition elements (3d series). Why ?

(iii) Identify the following :

(I) Oxoanion of chromium which is stable in acidic medium.

(II) The lanthanoid element that exhibits +4 oxidation state.

(iv) Write the products obtained on heating KMnO₄.

(v) Predict which of the following ions will be coloured in aqueous solution :

Cu⁺, Sc³⁺, Fe²⁺, Ti³⁺, Zn²⁺

(i) How will you bring about the following conversions :

(I) Bromobenzene to 1-phenylethanol

(II) Benzene to m-nitroacetophenone

(ii) An organic compound with the molecular formula C₈H₈O forms 2,4-DNP derivative, reduces Tollens’ reagent and undergoes Cannizzaro reaction. On vigorous oxidation with acidic or alkaline KMnO₄ it gives Benzene-1,2-dicarboxylic acid. Identify the compound and write the products when it undergoes Cannizzaro reaction.

(iii) Arrange the following compounds in increasing order of their acid strength :

C₆H₅COOH, O₂N – CH₂ – COOH, CF₃ – COOH, HCOOH

(i) Write the products formed when benzaldehyde reacts with the following reagents :

(I) 2,4-Dinitrophenylhydrazine

(II) Acetophenone in the presence of dilute NaOH followed by heating

(ii) Give reasons for the following :

(I) Benzoic acid does not undergo Friedel-Crafts reaction.

(II) Carboxylic acids have higher boiling point than alcohols of comparable molecular mass.

(iii) Write simple chemical test to distinguish between propanal and propanone.

(i) Calculate E°_cell for the following reaction which is at equilibrium :

Cu (s) + 2Ag⁺ (aq) ⇌ Cu²⁺ (aq) + 2Ag (s)

Equilibrium constant (K_c ) for the cell is 10¹⁵.

[Given : log 10 = 1]

(ii) Write anode, cathode and overall reaction of lead storage battery when it is in use.

(iii) How much electricity is required in coulombs for the oxidation of 1 mol of FeO to Fe₂O₃?

(i) Conductivity of 0·0024 M acetic acid is 7·2 × 10⁻⁵ S cm⁻¹. If Λ°ₘ for acetic acid is 390·5 S cm² mol⁻¹, then calculate the degree of dissociation (α) of acetic acid.

(ii) Calculate the cell potential for the following half cell reaction at 25ºC :

Ag⁺(aq) + 1 e⁻ → Ag (s)

Given that : [Ag⁺ ] = 0·01 M and

E°_Ag⁺/Ag = + 0·80 V

[log 10 = 1]

(iii) Write the name of the electrolyte used in :

(I) Dry cell

(II) Fuel cell (H₂ – O₂)