CBSE Class 12 2025 Chemistry 56-7-3 Question Paper Set-3: Download Solutions with Answer Key

With increase in atomic number, the melting point of transition metals:

• (A) first increases and then decreases
• (B) increases continuously
• (C) first decreases and then increases
• (D) remains constant

Which of the following aqueous solutions will have the highest osmotic pressure?

• (A) 1% KCl
• (B) 1% glucose
• (C) 1% urea
• (D) 1% CaCl₂

A conductivity cell usually consists of two:

• (A) Copper electrodes
• (B) Platinum electrodes
• (C) Zinc electrodes
• (D) Iron electrodes

Which of the following is the slope of the first order reaction in the plot of ln[R] vs. time?

• (A) +k
• (B) +k/2.303
• (C) -k
• (D) -k/2.303

Which of the following represents the fraction of molecules with energies equal to or greater than E_a?

• (A) −E_a/RT
• (B) e^−E_a/RT
• (C) e^+E_a/RT
• (D) +E_a/RT

The number of moles of AgCl precipitated when excess AgNO\(_3\) solution is mixed with one mole of \( \mathrm{[Co(NH_3)_6]Cl_3} \) is :

• (A) 0
• (B) 3
• (C) 6
• (D) 4

Which of the following haloalkanes is most reactive towards S_N2 reaction?

• (A) CH₃-CH₂-I
• (B) CH₃-CH₂-Br
• (C) CH₃-CH₂-Cl
• (D) CH₃-CH₂-F

The reaction

suggests that phenol is :

• (A) Basic
  
• (B) Neutral
  
• (C) Acidic
  
• (D) Amphoteric
  

Phenol reacts with conc. \(\mathrm{HNO_3}\) to form :

• (A) Salicylic acid
• (B) Picric acid
• (C) Benzoic acid
• (D) Phthalic acid

Anilinium hydrogen sulphate on heating at 453 - 473 K produces which of the following as a major product?

• (A) 2-aminobenzene sulphonic acid
• (B) benzene sulphonic acid
• (C) 2-aminobenzoic acid
• (D) sulphanilic acid

Which of the following amines does not give foul smell of isocyanide on heating with chloroform and ethanolic KOH ?

• (A) a
• (B) b
• (C) c
• (D) d

Deficiency of vitamin B₁ causes the disease:

• (A) Convulsions
• (B) Beri-Beri
• (C) Fissuring at corners of mouth and lips (Cheilosis)
• (D) Muscular weakness

Assertion (A): A mixture of o-nitrophenol and p-nitrophenol can be separated by fractional distillation.

Reason (R): o-nitrophenol is steam volatile due to intramolecular hydrogen bonding.

• (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): Aquatic species are more comfortable in cold water than in warm water.

Reason (R): Solubility of oxygen gas in water decreases with increase in temperature.

• (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): First ionisation enthalpy of Cr is lower than that of Zn.

Reason (R): Zinc is a non-transition element.

• (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): Vitamin C cannot be stored in our body.

Reason (R): Vitamin C is water soluble and excreted in urine.

• (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.

(a) A and B liquids on mixing show rise in temperature. Which type of deviation from Raoult's law is there and why?

(b) Why can azeotropic mixture not be separated by fractional distillation?

Why is molecularity applicable only for elementary reactions and order is applicable for elementary as well as complex reactions?

Write two differences between DNA and RNA.

Write the IUPAC name of the complex [Pt(en)₂Cl₂]²⁺. Draw the structure of geometrical isomer of this complex which is optically inactive.

Write the formula of the following coordination compound: Pentaamminecarbonatocobalt(III) chloride.

Why are haloarenes less reactive towards nucleophilic substitution reaction? How does the presence of nitro (-NO₂) group at ortho- and para-positions in haloarenes increase the reactivity towards nucleophilic substitution reaction?

Write the name of the cell which is generally used in inverters. Write the reactions taking place at anode and cathode of this cell, when it is in use.

Explain why electrolysis of an aqueous solution of NaCl gives \( \mathrm{H_2} \) gas at cathode and \( \mathrm{Cl_2} \) gas at anode ? Write overall reaction.
(Given : \( E^\circ_{\mathrm{Na^+/Na}} = -2.71 \ \mathrm{V} \), \( E^\circ_{\mathrm{H_2O/H_2}} = -0.83 \ \mathrm{V} \), \( E^\circ_{\mathrm{Cl_2/2Cl^-}} = +1.36 \ \mathrm{V} \), \( E^\circ_{\mathrm{H^+/O_2/H_2O}} = +1.23 \ \mathrm{V} \))

0.3 g of acetic acid (Molar mass = 60 g mol^-1) dissolved in 30 g of benzene shows a depression in freezing point equal to 0.45°C. Calculate the percentage association of acid if it forms a dimer in the solution.

(Given: K_f for benzene = 5.12 K kg mol^-1)

A compound (A) with molecular formula C₄H₉I which is a primary alkyl halide, reacts with alcoholic KOH to give compound (B). Compound (B) reacts with HI to give (C) which is an isomer of (A). When (A) reacts with Na metal in the presence of dry ether, it gives a compound (D), C₈H₁₈, which is different from the compound formed when n-butyl iodide reacts with sodium. Write the structures of (A), (B), (C) and (D). Write the chemical equation when compound (A) is reacted with alcoholic KOH.

The following data were obtained during the first order thermal decomposition of \( \text{N}_2\text{O}_5(g) \) at constant volume:

Write the reaction of D-Glucose with the following:

(a) HCN

(b) Br₂ water

(c) (CH₃CO)₂O

Write structure of the products of the following reactions:

Give reasons for the following:

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

(b) HCHO is more reactive than CH₃CHO towards addition of HCN.

(c) Vinyl group directly attached with carboxylic acid should decrease the acidity of corresponding carboxylic acid due to resonance, but on the contrary it increases the acidity.

The Crystal Field Theory (CFT) of coordination compounds is based on the effect of different crystal fields (provided by the 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. In tetrahedral coordination entity formation, the d-orbital splitting is smaller as compared to the octahedral entity.
On the basis of CFT, explain why \( \mathrm{[Ti(H_2O)_6]Cl_3} \) complex is coloured ? What happens on heating the complex \( \mathrm{[Ti(H_2O)_6]Cl_3} \) ? Give reason.
[Atomic no. : Ti = 22]

What is crystal field splitting energy?

On the basis of \(\Delta_0\) and P (pairing energy), how can you differentiate between a strong field ligand and a weak field ligand?

Why are low spin tetrahedral complexes rarely observed?

Amines are usually formed from amides, imides, halides, nitro compounds, etc. They exhibit hydrogen bonding which influences their physical properties. In alkyl amines, a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines. Alkyl amines are found to be stronger bases than ammonia. Amines being basic in nature, react with acids to form salts. Aryldiazonium salts, undergo replacement of the diazonium group with a variety of nucleophiles to produce aryl halides, cyanides, phenols and arenes.

Answer the following questions:

How can you convert the following?

(i) Ethanoic acid to methanamine

(ii) Propanenitrile to 1-aminopropane

Why is the \(pK_b\) of aniline greater than that of methylamine?

Amines are usually formed from amides, imides, halides, nitro compounds, etc. They exhibit hydrogen bonding which influences their physical properties. In alkyl amines, a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines. Alkyl amines are found to be stronger bases than ammonia. Amines being basic in nature, react with acids to form salts. Aryldiazonium salts, undergo replacement of the diazonium group with a variety of nucleophiles to produce aryl halides, cyanides, phenols and arenes.

Arrange the following in increasing order of their basic strength in aqueous solution:
CH\(_3\)–NH\(_2\), (CH\(_3\))\(_2\)NH, (CH\(_3\))\(_3\)N

(c) (ii) Give the structures of A and B in the following reaction:

C₆H₅NO₂ ⟶[Fe/HCl] A ⟶[HNO₂/273 K] B

An organic compound (X) having molecular formula \( \mathrm{C_5H_{10}O} \) can show various properties depending on its structures. Draw each of the structures if it :
(I) shows Cannizzaro reaction.
(II) reduces Tollens' reagent and has a chiral carbon.
(III) gives positive iodoform test.

Answer the following questions:

(i) Draw structure of the methyl hemiacetal of methanal.

(ii) There are two -NH₂ groups in semicarbazide. However only one is involved in the formation of semicarbazones. Give reason.

(iii) How will you convert ethanol to 3-hydroxybutanal?

(iv) Complete the following equation:

Cyclohexanol ⟶[CrO₃] ?

(v) Write the final product formed when phthalic acid is treated with NH₃ followed by strong heating.

Calculate the emf of the following cell at 25\(^\circ\)C :
Zn(s) \(\mid\) Zn\(^{2+}\) (0.1 M) \(\parallel\) H\(^+\) (0.01 M) \(\mid\) H\(_2\)(g) (1 bar), Pt(s)
Given: E\(^\circ_{Zn^{2+}/Zn}\) = –0.76 V, E\(^\circ_{2H^+/H_2}\) = 0.00 V, log 10 = 1

State Faraday's second law of electrolysis. How much electricity is required in terms of Faraday for the reduction of 1 mol of Cr₂O₇^2- to Cr³⁺?

The conductivity of a 0.2 M solution of KCl is \( 2.48 \times 10^{-2} \) S cm\(^{-1}\). Calculate its molar conductivity and degree of dissociation (\( \alpha \)).
Given: \( \lambda^0_{\text{K}^+} = 73.5 \, \text{S cm}^2 \text{mol}^{-1} \), \( \lambda^0_{\text{Cl}^-} = 76.5 \, \text{S cm}^2 \text{mol}^{-1} \)

Calculate \(\Delta_rG^\circ\) of the following cell :

\( \mathrm{Mg(s) + Cu^{2+}(aq) \longrightarrow Mg^{2+}(aq) + Cu(s)} \)

[Given : \( E^\circ_{\mathrm{Mg^{2+}/Mg}} = -2.37\ \mathrm{V} \), \( E^\circ_{\mathrm{Cu^{2+}/Cu}} = +0.34\ \mathrm{V} \), \( 1\ \mathrm{F} = 96500\ \mathrm{C\ mol^{-1}} \)]

What type of cell is mercury cell? Why is it more advantageous than dry cell?

(i) Account for the following:

(I) The E°_Mn²⁺/Mn value for manganese is highly negative, whereas E°_{Mn³⁺/Mn²⁺} is highly positive.

(II) Actinoids show wide range of oxidation states.

(III) Transition metals have high melting points.

(ii) Complete the following ionic equations:

(I) 5SO₃^2- + 2MnO₄^- + 6H⁺ →

(II) 2MnO₄^- + H₂O + I^- →

Answer the following questions:

(i) Name two elements of 3d series for which the third ionisation enthalpies are quite high.

(ii) Out of KMnO₄ and K₂MnO₄, which one is paramagnetic and why?

(iii) Write any one consequence of lanthanoid contraction.

(iv) How do you prepare potassium manganate from pyrolusite ore?

(v) Why is the ability of oxygen more than fluorine to stabilise higher oxidation states of transition metals?