CBSE Class 12 2025 Chemistry 56-4-1 Question Paper Set-1: Download Solutions with Answer Key

In an electrochemical cell, the following reaction takes place : \(2Cu^{2+} (aq) + Zn (s) \rightarrow 2Cu (s) + Zn^{2+} (aq)\)
\(E^\circ_{cell} = 1.28 \, V\)

As the reaction progresses, what will happen to the overall voltage of the cell?

• (A) Voltage will remain constant.
• (B) It will decrease as \([Zn^{2+}]\) increases.
• (C) It will increase as \([Cu^+]\) increases.
• (D) It will increase as \([Zn^{2+}]\) increases.

Out of Fe\(^{3+}\), Sc\(^{3+}\), Cr\(^{3+}\) and Co\(^{3+}\) ions, the one which is colourless in aqueous solution is:

• (A) Sc\(^{3+}\)
• (B) Fe\(^{3+}\)
• (C) Cr\(^{3+}\)
• (D) Co\(^{3+}\)

Hoffmann Bromamide degradation reaction is given by:

• (A) ArNO\(_2\)
• (B) ArNH\(_2\)
• (C) ArCONH\(_2\)
• (D) ArCH\(_2\)NH\(_2\)

In the Haworth structure of the following carbohydrate, various carbon atoms have been numbered. The anomeric carbon is numbered as:

• (A) 1
• (B) 2
• (C) 3
• (D) 5

The value of Henry's constant K\(_H\) is:

• (A) greater for gases with higher solubility
• (B) greater for gases with lower solubility
• (C) constant for all gases
• (D) not related to the solubility of gases

Out of the following statements, the incorrect statement is:

• (A) La is actually an element of transition series.
• (B) Zr and Hf have almost identical atomic radii because of lanthanoid contraction.
• (C) Ionic radius decreases from La\(^{3+}\) to Lu\(^{3+}\) ion.
• (D) Lanthanoids are radioactive in nature.

Out of 2-Bromobutane, 1-Bromobutane, 2-Bromopropane and 1-Bromopropane, the molecule which is chiral in nature is:

• (A) 2-Bromobutane
• (B) 1-Bromobutane
• (C) 2-Bromopropane
• (D) 1-Bromopropane

In the given reaction sequence, the structure of Y would be:

The product of the oxidation of I\(^-\) with MnO\(_4^-\) in alkaline medium is:

• (A) IO\(_4^-\)
• (B) I\(_2\)
• (C) IO\(^-\)
• (D) IO\(_3^-\)

Polyhalogen compounds have wide application in industries and agriculture. DDT is also a very important polyhalogen compound. It is a:

• (A) greenhouse gas
• (B) fertilizer
• (C) biodegradable insecticide
• (D) non-biodegradable insecticide

What amount of electric charge is required for the reduction of 1 mole of MnO\(_4^{2-}\) into Mn\(^{2+}\)?

• (A) 1F
• (B) 5F
• (C) 4F
• (D) 6F

Alkenes are formed by heating alcohols with conc. H\(_2\)SO\(_4\). The first step in the reaction is:

• (A) formation of carbocation
• (B) formation of ester
• (C) protonation of alcohol molecule
• (D) elimination of water

Assertion (A): Electrolysis of aqueous NaCl gives H\(_2\) at cathode and Cl\(_2\) at anode.

Reason (R): Chlorine has higher oxidation potential than H\(_2\)O.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): Cuprous salts are diamagnetic.

Reason (R): Cuprous ion has completely filled 3d-orbitals.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): n-Butyl chloride has higher boiling point than n-Butyl bromide.

Reason (R): C—Cl bond is more polar than C—Br bond.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Assertion (A): Acetanilide is less basic than aniline.

Reason (R): Acetylation of aniline results in decrease of electron density on nitrogen.

• (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• (C) Assertion (A) is true, but Reason (R) is false.
• (D) Assertion (A) is false, but Reason (R) is true.

Reactant ‘A’ underwent a decomposition reaction. The concentration of ‘A’ was measured periodically and recorded in the table given below:

Based on the above data, predict the order of the reaction and write the expression for the rate law.

The reaction between H\(_2\) (g) and I\(_2\) (g) was carried out in a sealed isothermal chamber. The rate law for the reaction was found to be: \[ Rate = k[H_2][I_2] \]
If 1 mole of H\(_2\) (g) was added to the reaction chamber and the temperature was kept constant, then predict the change in rate of the reaction and the rate constant.

PCl\(_3\), 2KCl does not give precipitate of AgCl with AgNO\(_3\) solution. Write the structural formula and IUPAC name of the complex.

Define fuel cell. Give two advantages of fuel cell over ordinary cell.

Write the structures of the main products of the following reactions:





(a) CH\(_3\)CH\(_2\)-C\(\equiv\)O + NaBH\(_4\)

(b) 6CH\(_3\)C\(\equiv\)O + 2AlCl\(_3\) \(\rightarrow\) 6CH\(_3\)C\(\equiv\)O

What is meant by essential amino acids? Why are amino acids amphoteric in nature?

Account for the following:
(i) Allyl chloride is hydrolyzed more readily than n-propyl chloride.

(ii) Isocyanides are formed when alkyl halides are treated with silver cyanide.

(iii) Methyl chloride reacts faster with OH\(^-\) ion in \(S_N2\) reaction than t-butyl chloride.

Complete the following reactions by writing the structural formulae of ‘A’ and ‘B’:

(i) CH\(_3\)CH=CH\(_2\) + HBr \(\xrightarrow{Peroxide}\) ‘A’ \(\xrightarrow{KOH}\) ‘B’

(ii) CH\(_3\)CH\(_2\)CHCl + alc. KOH \(\xrightarrow{\Delta}\) ‘A’ \(\xrightarrow{H_2O}\) ‘B’ (Main product)

Calculate the cell voltage of the voltaic cell which is set up by joining following half-cells at 25°C:

Al/Al\(^{3+}\)(0.001 M) and Ni/Ni\(^{2+}\)(0.1 M)

Given: \(E^\circ_{Al} = -1.66\) V, \(E^\circ_{Ni} = -0.25\) V, \(n_{Al} = 3\), \(n_{Ni} = 2\)

Give explanation for each of the following observations:

(a) With the same d\(^8\) orbital configuration, Mn\(^{2+}\) ion is an oxidizing agent whereas Cr\(^{2+}\) ion is a reducing agent.

(b) Atomic contraction is greater from element to element than much from lanthanides.

(c) Transition metals form large number of interstitial compounds with H, B, C, and N.

An aqueous solution of NaOH was made and its molar mass from the measurement of osmotic pressure at 27°C was found to be 25 g mol\(^{-1}\).

Calculate the percentage dissociation of NaOH in this solution.

Arrange the following compounds as asked:

(a) In decreasing order of pKb, values:
C\(_6\)H\(_5\)NH\(_2\), (C\(_2\)H\(_5\))\(_2\)NH, C\(_6\)H\(_5\)NHCH\(_2\)CH\(_3\), C\(_6\)H\(_5\)NH\(_3\)


(b) Increasing order of boiling point:
C\(_6\)H\(_5\)OH, C\(_2\)H\(_5\)NH\(_2\), (C\(_2\)H\(_5\))\(_2\)NH, C\(_6\)H\(_5\)NH\(_2\)


(c) Increasing order of solubility in water:
C\(_6\)H\(_5\)NH\(_2\), (C\(_2\)H\(_5\))\(_2\)NH, C\(_6\)H\(_5\)NHCH\(_2\)CH\(_3\)

An aromatic compound A\(^1\) with molecular formula C\(_8\)H\(_8\)O gives positive 2,4-DNP test. It gives yellow precipitate of compound ‘B’ on treatment with sodium hypobromite. Compound ‘A’ does not react with Tollen’s or Fehling’s reagent; on drastic oxidation with KMnO\(_4\), it forms a carboxylic acid ‘C’. Elucidate the structures of A, B and C. Also give their IUPAC names.

(a) Can sodium ethoxide and t-butyl chloride be used for the preparation of t-butyl ethyl ether? Give suitable explanation. Justify your answer by suggesting the appropriate starting material required for preparation of t-butyl ethyl ether.

Give the IUPAC name of above mentioned ether.

According to the generally accepted definition of the ideal solution there are equal interaction forces acting between molecules belonging to the same or different species. (This is equivalent to the statement that the activity of the components equals the concentration.) Strictly speaking, this concept is valid in ecological systems (isotopic mixtures of an element, hydrocarbons mixtures, etc.). It is still usual to talk about ideal solutions as limiting cases in reality since very dilute solutions behave ideally with respect to the solvent. This law is further supported by the fact that Raoult’s law empirically found for describing the behaviour of the solvent in dilute solutions can be deduced thermodynamically via the assumption of ideal behaviour of the solvent.


Answer the following questions:


(a) Give one example of miscible liquid pair which shows negative deviation from Raoult’s law. What is the reason for such deviation?

Ribose and 2-deoxyribose have an important role in biology. Among the most important derivatives are those with phosphate groups attached at the 5 position. Mono-, di- and tri-phosphate forms are important, as well as 3-5 cyclic monophosphates. Purines and pyrimidines form an important class of compounds with ribose and deoxyribose. When these purine and pyrimidine derivatives are coupled to a ribose sugar, they are called nucleosides.

Answer the following questions :
(a) What products would be formed when DNA is hydrolyzed? How is DNA different from RNA with reference to structure?

(a) (i) Complete the following reactions by writing the structure of the main products:

(b) (i) Complete each synthesis by giving missing starting material, reagent, or products:

(I) \(CH_3CH_3 + KMnO_4, KOH \longrightarrow ?\)

(ii) Carry out the following conversions:
(I) Benzaldehyde to Benzophenone

(a) Give reasons:

(I) \([ Ni(CO)_4 ]\) is diamagnetic whereas \([ NiCl_4 ]^{2-}\) is paramagnetic. [Atomic number: Ni = 28]

(II) CO is a stronger complexing agent than NH\(_3\).

(III) The trans isomer of complex \([ Co(en)_2Cl_2 ]^{+}\) is optically inactive.

(a) (i) The initial concentration of N\(_2\)O\(_5\) in the first-order reaction:
\[ N_2O_5 (g) \rightarrow 2 NO_2 (g) + \frac{1}{2} O_2 (g) \]
was \( 1.2 \times 10^{-2} \) mol L\(^{-1}\). The concentration of N\(_2\)O\(_5\) after 60 minutes was \( 0.2 \times 10^{-2} \) mol L\(^{-1}\). Calculate the rate constant of the reaction at 318 K.
\([ \log 6 = 0.778 ]\)

(ii) Account for the following:

(I) We cannot determine the order of a reaction by taking into consideration the balanced chemical equation.

(II) A bimolecular reaction may become kinetically first order under a specified condition.