CBSE Class 12 Chemistry Guess Paper 2027

In the ring structure of fructose, the anomeric carbon is : (A) C2 (B) C3 (C) C4 (D) C1

Assertion (A): Starch forms colloidal solution with water. Reason (R): Starch contains 80-85% of amylopectin which is insoluble in water. Select the most appropriate answer from the options given below: A. Both A and R are true, and R is the correct explanation of A. B. Both A and R are true, and R is not the correct explanation of A. C. A is true but R is false. D. A is false but R is true

The correct IUPAC name of [Pt(NH₃)₂Cl₂]²⁺ is (A) Diamminedichloridoplatinum (II) (B) Diamminedichloridoplatinum (IV) (C) Diamminedichloridoplatinum (O) (D) Diamminedichloridoplatinate (IV)

The magnetic moment is associated with its spin angular momentum and orbital angular momentum. Spin only magnetic moment value of Cr³⁺ ion (Atomic no. : Cr = 24) is ________. (A) 2.87 B.M. (B) 3.87 B.M. (C) 3.47 B.M. (D) 3.57 B.M.

The organic compounds A, B and C are amines having equivalent molecular weight. A and B on reaction with benzene sulphonyl chloride give white precipitate, however white precipitate obtained from compound B remains insoluble in NaOH. The variation in the boiling point of A, B and C can be seen as : A. A> B>C B. B>A>C C. A=B > C D. C>B>A

Assertion (A) : p-nitrophenol is less acidic than phenol. Reason (R) : Nitro group is an electron-withdrawing group, which stabilises the phenoxide ion.

Acetamide reacts with Br₂ and aqueous KOH to form : (A) Ethanamine (B) Ammonia (C) Methanamine (D) Ethanenitrile

Arrange the following compounds in increasing order of their boiling points: (i) (CH₃)₂CH-CH₂Br (ii) CH₃CH₂CH₂CH₂Br (iii) (CH₃)₃C-Br The correct order is (A) (ii) < (i) < (iii) (B) (i) < (ii) < (iii) (C) (iii) < (i) < (ii) (D) (iii) < (ii) < (i)

The name inner transition metals is often used to refer to the A. lanthanoids B. actinoids C. both lanthanoids and actinoids D. d block elements

For an electrolyte consisting of a monovalent cation and a monovalent anion undergoing dissociation in water, the van't Hoff factor (i) is : (A) less than 1 (B) equal to 1 (C) greater than 1 (D) greater than 2

70 gm solute is dissolved in 700 gm solvent to prepare a solution having density 1.5 g/ml. The ratio of its molality and molarity will be: A. 0.77 B. 1.4 C. 0.73 D. 1.3

Match the column I and column II: Column I (reactions of organic halides/alcohols shown as structures) with Column II: (i) Addition reaction, (ii) Elimination reaction, (iii) S_N² reaction, (iv) S_N¹ reaction. A. A-(i), B-(ii), C-(iii), D-(iv) B. A-(iv), B-(ii), C-(iii), D-(i) C. A-(i), B-(iii), C-(ii), D-(iv) D. A-(iv), B-(iii), C-(ii), D-(i)

Formulation of Cobalt(III) Chloride-Ammonia Complexes: Colour / Formula / Solution conductivity corresponds to Yellow / [Co(NH₃)₆]³⁺ 3Cl^- / Y Purple / [CoCl(NH₃)₅]²⁺ 2Cl^- / 1:2 electrolyte Green / X / 1:1 electrolyte 'X' and 'Y' in the above table are: a. X=[Co(NH₃)₆]²⁺ 3Cl^-, Y= 1:3 b. X= [Co(NH₃)₄Cl₂]^+ Cl^-, Y= 1:3 c. X=[Co(NH₃)₄Cl₂]^+ Cl^-, Y= 1:1 d. X=[Co(NH₃)₄Cl₂]³⁺ 3Cl^-, Y= 1:1

Which of the following will give a yellow or orange ppt. with 2,4 DNP? (i) Porpanal (ii) Propanone (iii) Propanoic acid A. (i) and (ii) B. (ii) and (iii) C. (i) and (iii) D. (i), (ii) and (iii)

Assertion (A): The pK_a of ethanoic acid is lower than that of Cl-CH_2-COOH. Reason (R): Chlorine shows electron withdrawing (-I) effect which increases the acidic character of Cl-CH_2-COOH. Select the correct answer: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true, but R is not the correct explanation of A. (C) A is true, but R is false. (D) A is false, but R is true.

Assertion (A): The boiling point of ethanol is higher than that of methoxymethane. Reason (R): There is intramolecular hydrogen bonding in ethanol. (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.

Write the reactions involved when D-glucose is treated with the following reagents: (a) HCN (b) Br₂ water

Define the following terms : (a) Ambidentate ligand (b) Crystal field splitting energy

On diluting two electrolytes 'A' and 'B', the Λ_m of 'A' increases 25 times while that of 'B' increases by 1.5 times. Which of the two electrolytes is strong ? Justify your answer graphically.

Write the Nernst equation for the following cell reaction : Zn(s) + Cu²⁺ (aq) -> Zn²⁺ (aq) + Cu(s). How will the E_cell be affected when concentration of (i) Cu²⁺ ions is increased and (ii) Zn²⁺ ions is increased ?

Complete the following reactions by writing the major and minor product in each case (any 2) a. CH₃CH₂Br + KCN -> b. CH₃CH₂CH = CH₂ + HBr -> c. (CH₃)₂CHCHClCH₃ + alc KOH ->

The elements of 3d transition series are given as: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. Answer the following: (a) Copper has exceptionally positive E°_M²⁺/M value, why? (b) Which element is a strong reducing agent in +2 oxidation state and why? (c) Zn²⁺ salts are colourless. Why?

(a) What is the difference between native protein and denatured protein? (b) Which one of the following is a disaccharide? Glucose, Lactose, Amylose, Fructose (c) Which vitamin is responsible for the coagulation of blood?

(i) Write the hybridisation and magnetic behaviour of the following complexes : (I) [Ni(CN)₄]^2- (II) [FeF₆]^3- (ii) What type of isomerism is shown by [Co(NH₃)₅(NO₂)]²⁺ and [Co(NH₃)₅(ONO)]²⁺ ? [Given : Atomic number : Ni = 28, Fe = 26]

The equilibrium constant of cell reaction: Sn⁴⁺(aq) + Al(s) -> Al³⁺ + Sn²⁺(aq) is 4.617 x 10¹⁸⁴, at 25 °C a. Calculate the standard emf of the cell. (Given: log 4.617 x 10¹⁸⁴ = 184.6644) b. What will be the E° of the half cell Al³⁺/Al, if E° of half cell Sn⁴⁺/Sn²⁺ is 0.15 V.

Answer the following questions: I. Are the enthalpies of atomisation of Zinc and Copper matched correctly? Justify your answer. (Enthalpy of atomisation / kJmol^-1: Zinc 339, Copper 130) II. Out of sulphuric acid and hydrochloric acid, which acid will you prefer for permanganate titrations and why? III. 5NO₂^- + 2MnO₄^- + 6H^+ -> (complete the equation)

A certain reaction is 50% complete in 20 minutes at 300 K and the same reaction is 50% complete in 5 minutes at 350 K. Calculate the activation energy if it is a first order reaction. [R = 8.314 J K^-1 mol^-1; log 4 = 0.602]

Various isomeric haloalkanes with the general formula C₄H₉Cl undergo hydrolysis reaction. Among them, compound "A" is the most reactive through S_N1 mechanism. Identify "A" citing the reason for your choice. Write the mechanism for the reaction.

[Case: Phenols undergo electrophilic substitution reactions readily due to the strong activating effect of OH group attached to the benzene ring. Since, the OH group increases the electron density more to o- and p- positions therefore OH group is ortho, para-directing. Reimer-Tiemann reaction is one of the examples of aldehyde group being introduced on the aromatic ring of phenol, ortho to the hydroxyl group. This is a general method used for the ortho-formylation of phenols.] Answer the following questions: (a) What happens when phenol reacts with (i) Br₂/CS₂ (ii) Conc. HNO₃ (b) Why phenol does not undergo protonation readily? (c) Which is a stronger acid - phenol or cresol? Give reason. OR (c) Write the IUPAC name of the product formed in the Reimer-Tiemann reaction.

[Case: The rate of a chemical reaction is expressed either in terms of decrease in the concentration of reactants or increase in the concentration of a product per unit time. Rate of the reaction depends upon the nature of reactants, concentration of reactants, temperature, presence of catalyst, surface area of the reactants and presence of light. Rate law states that the rate of reaction depends upon the concentration terms on which the rate of reaction actually depends, as observed experimentally. The sum of powers of the concentration of the reactants in the Rate law expression is called order of reaction while the number of reacting species taking part in an elementary reaction which must collide simultaneously in order to bring about a chemical reaction is called molecularity of the reaction.] Answer the following questions: (a) (i) What is a rate determining step? (ii) Define complex reaction. (b) What is the effect of temperature on the rate constant of a reaction? OR (b) Why is molecularity applicable only for elementary reactions whereas order is applicable for elementary as well as complex reactions? (c) The conversion of molecule X to Y follows second order kinetics. If concentration of X is increased 3 times, how will it affect the rate of formation of Y?

Attempt either A or B. A. Answer the following questions: I. Write the structure of expected product of Cannizzaro reaction of 2-chlorobenzaldehyde. II. How would the presence of -SO₃H group effect the basic strength of aniline. III. Convert acetic acid to ethanamine. IV. Write the steps to prepare Benzoic acid from Benzoyl chloride. V. Give a chemical test to distinguish between: propanal and propanone

(i) Write the Nernst equation and calculate the emf of the following cell at 298 K : Mg (s) | Mg²⁺ (0.001 M) || Cu²⁺ (0.0001 M) | Cu (s) Given : E^o_Mg²⁺/Mg = - 2.36 V, E^o_Cu²⁺/Cu = + 0.34 V [log 10 = 1] (ii) Define fuel cell and write its two advantages.

(i) Carry out the following conversions : (1) Ethanal to But-2-en-1-al (2) Propanoic acid to 2-chloropropanoic acid (ii) An alkene with molecular formula C₅H₁₀ on ozonolysis gives a mixture of two compounds 'B' and 'C'. Compound 'B' gives positive Fehling test and also reacts with iodine and NaOH solution. Compound 'C' does not give Fehling solution test but forms iodoform. Identify the compounds 'A', 'B' and 'C'.