CBSE 12th Chemistry Question Paper 2024 (Set 1) with Answers

Q1 mcq 1 mark

Which one of the following first row transition elements is expected to have the highest third ionization enthalpy ?

A. Iron (Z = 26)
B. Manganese (Z = 25)
C. Chromium (Z = 24)
D. Vanadium (Z = 23)

Correct Answer: B — Solution

The electronic configuration of Manganese (Mn, Z=25) is [Ar] 3d5 4s2. Removing two electrons (first and second ionization) leaves the stable half-filled 3d5 configuration. The third ionization involves removing an electron from this stable half-filled d-subshell, which requires significantly higher energy compared to the other elements listed, where the d-subshell is not half-filled or is more easily ionized.

Q2 mcq 1 mark

Which of the following compounds will give a ketone on oxidation with chromic anhydride (CrO3) ?

A. (CH3)2CH CH2OH
B. CH3CH2CH2OH
C. (CH3)3C OH
D. CH3 CH2 CH CH3 | OH

Correct Answer: D — Solution

Chromic anhydride (CrO3) in acidic medium is a strong oxidizing agent. Secondary alcohols are oxidized to ketones. (CH3)2CHCH2OH (primary) forms an aldehyde then acid; CH3CH2CH2OH (primary) forms an aldehyde then acid; (CH3)3COH (tertiary) is generally resistant to oxidation under these conditions; CH3CH2CH(OH)CH3 is a secondary alcohol, which undergoes oxidation to form butanone (a ketone).

Q3 mcq 1 mark

Two among the three components of DNA are -D-2-deoxyribose and a heterocyclic base. The third component is :

A. Adenine
B. Phosphoric acid
C. Sulphuric acid
D. Uracil

Correct Answer: B — Solution

The three components of a nucleotide (which makes up DNA) are a nitrogenous base (like Adenine, Guanine, Cytosine, or Thymine), a pentose sugar (2-deoxyribose in DNA), and a phosphate group (derived from phosphoric acid).

Q4 mcq 1 mark

For an electrolyte undergoing association in a solvent, the vfactor :

A. is always greater than one
B. has negative value
C. has zero value
D. is always less than one

Correct Answer: D — Solution

The van't Hoff factor (i) is defined as the ratio of observed colligative property to calculated colligative property. When a solute undergoes association, the number of particles in the solution decreases, causing the value of i to be less than one.

Q5 mcq 1 mark

For the reaction X + 2Y P, the differential form equation of the rate law is :

A. 2d P d Y = dt dt
B. d P d X = dt dt
C. + d X d P = dt dt
D. 2d Y + d P = dt dt

Correct Answer: B — Solution

For the reaction X + 2Y -> P, the rate of reaction is given by -d[X]/dt = -(1/2)d[Y]/dt = +d[P]/dt. Rearranging the terms related to X and P, we get -d[X]/dt = d[P]/dt.

Q6 short answer

The compound which undergoes SN1 reaction most rapidly is :

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Q7 mcq 1 mark

Acetic acid reacts with PCl5 to give :

A. Cl CH2 COCl
B. Cl CH2 COOH
C. CH3 COCl
D. CCl3 COOH

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Q8 mcq

The formation of cyanohydrin from an aldehyde is an example of :

A. nucleophilic addition
B. electrophilic addition
C. nucleophilic substitution
D. electrophilic substitution

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Q9 mcq

In the Arrhenius equation, when log k is plotted against 1/T, a straight line is obtained whose :

A. slope is A/R and intercept is Ea.
B. slope is A and intercept is Ea/R.
C. slope is Ea/RT and intercept is log A.
D. slope is 2·303 R/Ea and intercept is log A.

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Q10 mcq

The reaction of an alkyl halide with sodium alkoxide forming ether is known as :

A. Wurtz reaction
B. Reimer-Tiemann reaction
C. Williamson synthesis
D. Kolbe reaction

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Q11 mcq

The correct order of the ease of dehydration of the following alcohols by the action of conc. H2SO4 is :

A. (CH3)3C OH > (CH3)2CH OH > CH3CH2 OH
B. (CH3)2CH OH > CH3CH2 OH > (CH3)3C OH
C. CH3CH2 OH > (CH3)2CH OH > (CH3)3C OH
D. (CH3)2CH OH > (CH3)3C OH > CH3CH2 OH

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Q12 mcq

Which functional groups of glucose interact to form cyclic hemiacetal leading to pyranose structure ?

A. Aldehyde group and hydroxyl group at C 4
B. Aldehyde group and hydroxyl group at C 5
C. Ketone group and hydroxyl group at C 4
D. Ketone group and hydroxyl group at C 5

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Q13 short answer

Assertion (A) : When NaCl is added to water a depression in freezing point is observed. Reason (R) : NaCl undergoes dissociation in water.

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Q14 short answer

Assertion (A) : Separation of Zr and Hf is difficult. Reason (R) : Zr and Hf have similar radii due to lanthanoid contraction.

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Q15 short answer

Assertion (A) : The pKa of ethanoic acid is lower than that of Cl CH2 COOH. Reason (R) : Chlorine shows electron withdrawing (-I) effect which increases the acidic character of Cl CH2 COOH.

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Q16 short answer

Assertion (A) : Aniline is a stronger base than ammonia. Reason (R) : The unshared electron pair on nitrogen atom in aniline becomes less available for protonation due to resonance.

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Q17 short answer

Calculate the potential of Iron electrode in which the concentration of Fe2+ ion is 0·01 M. (Eº Fe2+/Fe = 0·45 V at 298 K) [Given : log 10 = 1]

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Q18 short answer

Define molecularity of the reaction. State any one condition in which a bimolecular reaction may be kinetically of first order.

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Q19 short answer 2 marks

What happens when D-glucose is treated with the following reagents ? (a) HI (b) Conc. HNO3

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Q20 short answer 2 marks

Draw the structures of major monohalo products in each of the following reactions :

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Q21 short answer 2 marks

Give reasons for the following : (i) Grignard reagent should be prepared under anhydrous conditions. (ii) Alkyl halides give alcohol with aqueous KOH whereas in the presence of alcoholic KOH, alkenes are formed.

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Q21 short answer 2 marks

Write the chemical equation when : (a) Butan-2-one is treated with Zn(Hg) and conc. HCl. (b) Two molecules of benzaldehyde are treated with conc. NaOH.

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Q22 short answer 3 marks

When a certain conductivity cell was filled with 0·05 M KCl solution, it has a resistance of 100 ohm at 25ºC. When the same cell was filled with 0·02 M AgNO3 solution, the resistance was 90 ohm. Calculate the conductivity and molar conductivity of AgNO3 solution. (Given : Conductivity of 0·05 M KCl solution = 1·35 * 10^2 ohm^-1 cm^-1)

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Q23 short answer 3 marks

The following initial rate data were obtained for the reaction : 2NO (g) + Br2 (g) -> 2NOBr (g). (a) What are the orders with respect to NO and Br2 in the reaction ? (b) Calculate the rate constant (k). (c) Determine the reaction rate when the concentration of NO and Br2 are 0·4 M and 0·2 M respectively.

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Q24 long answer 3 marks

(a) Write the formula for the following coordination compound : Potassium tetrahydroxidozincate (II). (b) Arrange the following complexes in the increasing order of conductivity of their solution : [Cr(NH3)5Cl]Cl2, [Cr(NH3)3Cl3], [Cr(NH3)6]Cl3. (c) Identify the type of isomerism exhibited by the following complexes : (i) [Co(NH3)5NO2]2+ (ii) [Co(en)3]Cl3

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Q25 mcq

(a) Which of the following is an allylic halide ?

A. (i) CH3 CH = CH Br
B. (ii) CH2 = CH CH CH3 | Br

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Q26 long answer 3 marks

(a) Write the mechanism of the following reaction : CH3CH2OH H 443 K CH2 = CH2. (b) Write the main product in each of the following reactions : (i) CH3 CH2 CH = CH2 (ii)

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Q27 short answer 3 marks

Answer the following : (any three) (a) What is peptide linkage ? (b) What type of bonds hold a DNA double helix together ? (c) Which one of the following is a polysaccharide ? Sucrose, Glucose, Starch, Fructose (d) Give one example each for water-soluble vitamins and fat-soluble vitamins.

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Q28 long answer 3 marks

Compound (A) (C6H12O2) on reduction with LiAlH4 gives two compounds (B) and (C). The compound (B) on oxidation with PCC gives compound (D) which upon treatment with dilute NaOH and subsequent heating gives compound (E). Compound (E) on catalytic hydrogenation gives compound (C). The compound (D) is oxidized further to give compound (F) which is found to be a monobasic acid (Molecular weight = 60). Identify the compounds (A), (B), (C), (D), (E) and (F).

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Reading Passage

29. Batteries and fuel cells are very useful forms of galvanic cell. Any battery or cell that we use as a source of electrical energy is basically a galvanic cell. However, for a battery to be of practical use it should be reasonably light, compact and its voltage should not vary appreciably during its use. There are mainly two types of batteries primary batteries and secondary batteries. In the primary batteries, the reaction occurs only once and after use over a period of time the battery becomes dead and cannot be reused again, whereas the secondary batteries are rechargeable. Production of electricity by thermal plants is not a very efficient method and is a major source of pollution. To solve this problem, galvanic cells are designed in such a way that energy of combustion of fuels is directly converted into electrical energy, and these are known as fuel cells. One such fuel cell was used in the Apollo space programme.

Q30 short answer 1 mark

How do primary batteries differ from secondary batteries?

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Q31 short answer 1 mark

The cell potential of Mercury cell is 1.35 V, and remains constant during its life. Give reason.

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Q32 short answer 2 marks

Write the reactions involved in the recharging of the lead storage battery.

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Q33 short answer 2 marks

Write two advantages of fuel cells over other galvanic cells.

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Reading Passage

30. The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometrical shapes of coordination compounds whereas for coordination compounds is based on the effect of different crystal fields (provided by ligands taken as point charges), on the degeneracy of d-orbital energies of the central metal atom/ion. The splitting of the d-orbitals provides different electronic arrangements in strong and weak crystal fields. The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. Coordination compounds find extensive applications in metallurgical processes, analytical and medicinal chemistry.

Q34 short answer 1 mark

What is crystal field splitting energy?

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Q35 short answer 1 mark

Give reason for the violet colour of the complex [Ti(H2O)6]3+ on the basis of crystal field theory.

Solution hidden

Reading Passage

The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometrical shapes of coordination compounds whereas for coordination compounds is based on the effect of different crystal fields (provided by ligands taken as point charges), on the degeneracy of d-orbital energies of the central metal atom/ion. The splitting of the d-orbitals provides different electronic arrangements in strong and weak crystal fields. The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. Coordination compounds find extensive applications in metallurgical processes, analytical and medicinal chemistry.

Q36 short answer 2 marks

[Cr(NH3)6]3+ is paramagnetic while [Ni(CN)4]2 is diamagnetic. Explain why. [Atomic No. : Cr = 24, Ni = 28]

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Q37 short answer 2 marks

Explain why [Fe(CN)6]3 is an inner orbital complex, whereas [Fe(H2O)6]3+ is an outer orbital complex. [Atomic No. : Fe = 26]

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Q38 short answer 1 mark

At the same temperature, CO2 gas is more soluble in water than O2 gas. Which one of them will have higher value of KH and why ?

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Q39 short answer 1 mark

How does the size of blood cells change when placed in an aqueous solution containing more than 0.9% (mass/volume) sodium chloride ?

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Q40 short answer 3 marks

1 molal aqueous solution of an electrolyte A2B3 is 60% ionized. Calculate the boiling point of the solution. (Given : Kb for H2O = 0.52 K kg mol 1)

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Q41 short answer 2 marks

The vapour pressures of A and B at 25ºC are 75 mm Hg and 25 mm Hg, respectively. If A and B are mixed such that the mole fraction of A in the mixture is 0.4, then calculate the mole fraction of B in vapour phase.

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Q42 short answer 2 marks

Define colligative property. Which colligative property is preferred for the molar mass determination of macromolecules ?

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Q43 short answer 1 mark

Why are equimolar solutions of sodium chloride and glucose not isotonic ?

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Q44 short answer 1 mark

N,N-diethyl-benzenesulphonamide is insoluble in alkali. Give reason.

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Q45 short answer 1 mark

Aniline does not undergo Friedel-Crafts reaction. Why?

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Q46 short answer 1 mark

Write a simple chemical test to distinguish between methylamine and aniline.

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Q47 short answer 1 mark

Write the chemical reaction involved in Gabriel phthalimide synthesis.

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Q48 short answer 1 mark

How will you convert aniline to p-bromoaniline ?

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Q49 short answer

Account for the following: The melting and boiling points of Zn, Cd and Hg are low.

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Q50 short answer

Account for the following: Of the d4 species, Cr2+ is strongly reducing while Mn3+ is strongly oxidizing.

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Q51 short answer

Account for the following: Eo value of Cu2+/Cu is + 0.34 V.

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Q52 short answer

Complete the following reaction :

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Q53 short answer

Write the structures of A and B in the following reaction : 3 2 NH Br + NaOH A B

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Q54 short answer 3 marks

Account for the following: (1) The melting and boiling points of Zn, Cd and Hg are low. (2) Of the d4 species, Cr2+ is strongly reducing while Mn3+ is strongly oxidizing. (3) Eo value of Cu2+/Cu is + 0.34 V.

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Q55 short answer 2 marks

Complete and balance the following chemical equations : (1) KMnO4 heat (2) 2 2 7 Cr + 6 I O + 14 H+

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Q56 short answer 5 marks

(b) (i) Out of Cu2Cl2 and CuCl2 , which is more stable in aqueous solution and why ? (ii) Write the general electronic configuration of f-block elements. (iii) Predict which of the following will be coloured in aqueous solution and why ? Sc3+, Fe3+, Zn2+ [Atomic number : Sc = 21, Fe = 26, Zn = 30] (iv) How can you obtain potassium dichromate from sodium chromate ? (v) Why do transition metals and their compounds show catalytic activities ?

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