CBSE Class 12 Chemistry 2026 — Set 56/3/1

In aqueous solution, Cr₂O₇²⁻ ion converts to which of the following in alkaline medium ? (A) Cr³⁺ (B) CrO₄²⁻ (C) CrO (D) CrO₃

The boiling point of an azeotropic mixture of water and ethanol is less than that of pure water and ethanol. The mixture shows : (A) positive deviation from Raoult's Law. (B) negative deviation from Raoult's Law. (C) no deviation from Raoult's Law. (D) that the solution is an ideal solution.

The mole fraction of a solute in 2.0 molal aqueous solution is : (A) 1.87 (B) 0.347 (C) 0.0347 (D) 0.00347

On electrolysis of very dilute aqueous solution of NaCl using platinum electrodes : (A) H₂ gas is evolved at anode. (B) Na is produced at cathode. (C) O₂ gas is evolved at anode. (D) H₂ gas is evolved at cathode.

For a reaction 3A arrow 2B, the rate of reaction +(d[B])/(dt) is equal to : (A) -(3)/(2)(d[A])/(dt) (B) -(2)/(3)(d[A])/(dt) (C) -(1)/(3)(d[A])/(dt) (D) +2(d[A])/(dt)

On hydrolysis, which of the following carbohydrates gives only glucose ? (A) Sucrose (B) Galactose (C) Lactose (D) Maltose

For Questions number 13 to 16, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below : (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) : Separation of Zr and Hf is difficult. Reason (R) : Because Zr and Hf lie in the same group of the periodic table.

Assertion (A) : Phenol is less acidic than 4-methylphenol. Reason (R) : The presence of an electron releasing group in phenol makes it less acidic. Options : (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) : Gabriel phthalimide synthesis is used for the preparation of primary aliphatic amines. Options : (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) : Order of reaction is applicable to elementary as well as complex reactions. Reason (R) : Order of a reaction is an experimental quantity. Options : (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.

For the compound having molecular formula C₄H₉Br, write : (a) the isomer which is most reactive towards SN1 displacement. (b) the isomer which, on reacting with Na metal in the presence of dry ether, gives 2,5-Dimethylhexane.

For a reaction A + B arrow Products, the rate law is : Rate = k[A][B]3/2 Write the overall order of the reaction. Can this reaction be an elementary reaction ? Give reason in support of your answer.

Explain why, on addition of 1 mol of KCl to 1 litre of water, the boiling point of water increases, while the addition of 1 mol of methyl alcohol to 1 litre of water decreases the boiling point.

(a) Write IUPAC names of the following compounds : (i) [PtCl₂(en)₂]SO₄ (ii) (NH₄)₂[CoF₄] OR (b) Define the following terms with a suitable example in each case : (i) Ambidentate ligand (ii) Double salt

How do you explain the following ? (a) Presence of a straight chain in glucose (b) Presence of five -OH groups in glucose which are attached to different carbon atoms

The half-life period of a radioactive element is 1.5 × 10¹⁰ years. Calculate the time in which the activity of the element is reduced to 75% of its original value. [Given : log 2 = 0.30, log 3 = 0.48, log 4 = 0.60]

State Kohlrausch's law of independent migration of ions. With the help of a curve, explain why it is not easy to determine Lambdam^° for weak electrolytes by extrapolating the concentration - molar conductivity curve, as it is for strong electrolytes.

An antifreeze solution is prepared by dissolving 31 g of ethylene glycol (Molar mass = 62 g mol⁻¹) in 600 g of water. Calculate the freezing point of the solution. (Kf for water = 1.86 K kg mol⁻¹)

(a) Answer the following questions about the complexes [NiCl₄]²⁻ and [Ni(CN)₄]²⁻ : (i) Write the hybridization involved in each case. (ii) Which of them is the inner orbital complex and which one is the outer orbital complex ? (iii) Compare their magnetic behaviour. [Atomic number : Ni = 28] OR (b) (i) Name two coordination compounds which are important in biological systems. (ii) What is meant by chelate effect ? Give an example. (iii) Why are low spin tetrahedral complexes rarely formed ?

Give reasons for the following : (a) Although chlorine is an electron-withdrawing group, yet it is ortho-, para-directing in electrophilic aromatic substitution reactions. (b) Aryl halides cannot be prepared by reacting phenol with concentrated halogen acids or phosphorus halides. (c) Chloroform is stored in closed dark coloured bottles.

How will you obtain the following from benzenediazonium chloride ? Give chemical equations involved : (a) Chlorobenzene (b) Benzene (c) Benzonitrile

An organic compound (A) with molecular formula C₃H₅N on reaction with C₆H₅MgBr followed by hydrolysis, gives a compound (B). Compound (B) forms an orange-red precipitate with 2,4-DNP reagent and does not give iodoform test. It neither reduces Tollens' or Fehling's reagent nor does it decolourise bromine water. On drastic oxidation with chromic acid it gives a carboxylic acid (C) having molecular formula C₇H₆O₂. Identify the compounds (A), (B) and (C). Write the reactions of compound (A) with C₆H₅MgBr followed by hydrolysis to give compound (B).

Living systems are made up of various complex biomolecules like carbohydrates, proteins, nucleic acids, lipids, etc. Proteins and carbohydrates are essential constituents of our food. In addition, some simple molecules like vitamins and mineral salts also play an important role in the functions of organisms. All proteins are polymers of α-amino acids. Proteins can be classified into two types on the basis of their molecular shape — Fibrous and Globular proteins. Vitamins are accessory food factors required in the diet. They are classified as fat-soluble and water-soluble. Deficiency of vitamins leads to many diseases. Nucleic acids are the polymers of nucleotides which in turn consist of a base, a pentose sugar and phosphate moiety. There are two types of nucleic acids — DNA and RNA. Nucleic acids are responsible for the transfer of characters from parents to offsprings. (a) Write the name of basic building units of proteins and nucleic acids. How can you differentiate between Fibrous and Globular proteins on the basis of their structures ? (b) (i) What products would be formed when a nucleotide from DNA containing thymine is hydrolyzed ? OR (b) (ii) Write one structural difference between DNA and RNA. (c) Give one example each of a fat-soluble vitamin and a water-soluble vitamin.

Alcohols have higher boiling points than other compounds, namely hydrocarbons, ethers and haloalkanes of comparable molecular masses. On oxidation, primary alcohols yield aldehydes with mild oxidizing agents and carboxylic acids with strong oxidizing agents. Secondary alcohols yield ketones on oxidation while tertiary alcohols are resistant to oxidation. Ethers may be prepared by dehydration of alcohols and Williamson synthesis. The C-O bond in ethers can be cleaved by hydrogen halides. The presence of -OH group in phenols activates the aromatic ring towards electrophilic substitution and directs the incoming group to ortho and para positions due to resonance effect. In presence of NaOH, phenol generates phenoxide ion which is even more reactive than phenol. Thus, in alkaline medium, phenol undergoes Kolbe's reaction. (a) Name the reagents used in the following reactions : (i) Oxidation of a primary alcohol to aldehyde (ii) Oxidation of a primary alcohol to carboxylic acid (b) Write the reaction involved in Kolbe's reaction. (c) (i) Why are tertiary alcohols resistant to oxidation ? OR (c) (ii) Write the products of the following reaction : (CH₃)₃C-O-C₂H₅ xrightarrowHI

(a) (i) Describe giving reason which one of the following pairs has the property indicated : (I) Fe or Cu - higher melting point (II) Ti³⁺ or Sc³⁺ - coloured in aqueous solution (III) Cr or Zn - higher third ionisation enthalpy (ii) Write the ionic equations for the oxidizing action of MnO₄^- in acidic medium with : (I) Fe²⁺ ion (II) I^- ion OR (b) (i) A black-brown coloured solid (A) when fused with KOH in the presence of air, produces a dark green coloured compound (B) which on electrolytic oxidation in alkaline medium gives a dark purple coloured compound (C). Identify (A), (B) and (C). Write the reactions involved. (ii) What happens when an acidic solution of the green compound (B) is allowed to stand for some time ? Also write the equation involved. What is this type of reaction called ?

(a) (i) Write the product(s) when : (I) One mol of ethanal is treated with 1 mol of CH₃OH in the presence of dry HCl gas. (II) Benzaldehyde is treated with conc. NaOH. (III) Ethanoic acid is heated in the presence of P₂O₅. (ii) Write a simple chemical test to distinguish between Ethanal and Propanal. (iii) Write the name of the reagent to transform Allyl alcohol to Propenal. OR (b) (i) Draw the structure of the semicarbazone of acetone. (ii) Why are α-hydrogen atoms of aldehydes and ketones acidic in nature ? (iii) Arrange the following compounds in increasing order of their reactivity towards HCN : CH₃COCH₃, CH₃CHO, (CH₃)₃C-oversetOunderset\|C-CH₃ (iv) Write the reaction involved in Etard reaction. (v) Write the product when Cyclohexanecarbaldehyde (C₆H₁₁CHO, a cyclohexane ring bearing a -CHO group) reacts with Zn(Hg)/conc. HCl.

(a) (i) Calculate the electrode potential of a half-cell for zinc electrode dipping in 0.01 M ZnSO₄ solution at 25^°C. Given : E^°Zn²⁺/Zn = -0.76 V [log 10 = 1] (ii) Write anode, cathode and overall reaction involved in dry cell. (iii) Equilibrium constant (Kc) is related to E^°cell, but not to Ecell. Why ? OR (b) (i) The conductivity of 0.001 M solution of acetic acid is 3.905 × 10⁻⁵ S cm⁻¹. Calculate its molar conductivity and degree of dissociation (α). Given : λ^°CH_3COO^- = 40.9 S cm² mol⁻¹ λ^°H^+ = 349.6 S cm² mol⁻¹ (ii) Give reasons for the following : (I) Why does a mercury cell deliver a constant voltage for its entire life ? (II) Why is it necessary to use salt bridge in a galvanic cell ?