CBSE EXAMINATION PAPER-2025

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 condition is fulfilled only in exceptional cases for mixtures (optical isomers, isotopic mixtures of an element, hydrocarbon mixtures). 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 view 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 :

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 :

In an electrochemical cell, the following reaction takes place :

2Cu⁺(aq) + Zn(s) → 2Cu(s) + Zn²⁺(aq)

E°cell = 1·28 V

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

Out of Fe³⁺, Sc³⁺, Cr³⁺ and Co³⁺ ions, the one which is colourless in aqueous solution is:

[Atomic number : Fe = 26, Sc = 21, Cr = 24, Co = 27]

Hoffmann Bromamide degradation reaction is given by:

The value of Henry’s constant Kₕ is:

Out of the following statements, the incorrect statement is:

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

The product of the oxidation of I⁻ with MnO₄⁻ in alkaline medium is:

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

What amount of electric charge is required for the reduction of 1 mole of MnO₄⁻ into Mn²⁺?

Alkenes are formed by heating alcohols with conc. H₂SO₄. The first step in the reaction is:

Assertion (A) : Cuprous salts are diamagnetic.

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

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.

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

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

Assertion (A) : Electrolysis of aqueous NaCl gives H₂ at cathode and Cl₂ at anode.

Reason (R) : Chlorine has higher oxidation potential than H₂O.

The reaction between H₂ (g) and I₂ (g) was carried out in a sealed isothermal container. The rate law for the reaction was found to be :

Rate =Rate = k[H₂][I₂]

If 1 mole of H₂ (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.

PtCl₄ . 2KCl doesn’t give precipitate of AgCl with AgNO₃ solution. Write the structural formula and IUPAC name of the complex.

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

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

Calculate the cell voltage of the voltaic cell which is set up by joining following half-cells at 25⁰C: Al/Al³⁺ (0·001 M) and Ni/Ni²⁺ (0·1 M)

Given : EᵒNi²⁺/ Ni = – 0·25 V, EᵒAl³⁺/Al = – 1·66 V

Give explanation for each of the following observations :

(a) With the same d-orbital configuration (d4), Mn3+ ion is an oxidising agent whereas Cr2+ ion is a reducing agent.

(b) Actinoid contraction is greater from element to element than that among lanthanoids.

(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 27⁰C was found to be 25 g mol⁻¹. Calculate the percentage dissociation of NaOH in this solution.

[Atomic mass : Na = 23 u, O = 16 u, H = 1 u]

Arrange the following compounds as asked : 3

(a) in decreasing order of pKb values C₂H₅NH₂, (C₂H₅)₂NH, C₆H₅NHCH₃, C₆H₅NH₂

(b) increasing order of boiling point C₂H₅OH, C₂H₅NH₂, (CH₃)₂NH

(c) increasing order of solubility in water C₆H₅NH₂, (C₂H₅)₂NH, C₂H₅NH₂

An aromatic compound ‘A’ with molecular formula C₈H₈O gives positive 2,4-DNP test. It gives yellow precipitate. of compound ‘B’ on treatment with sodium hypoiodite. Compound ‘A’ does not react with Tollen’s or Fehling’s reagent; on drastic oxidation with KMnO₄ it forms a carboxylic acid ‘C’. Elucidate the structures of A, B and C. Also give their IUPAC names.