List of top Questions asked in CBSE CLASS XII- 2026

Answer the following: \[ (a)(i)\;\text{Describe giving reason which one of the following pairs has the property indicated:} \] \[ (I)\;Fe\text{ or }Cu-\text{higher melting point} \] \[ (II)\;Ti^{3+}\text{ or }Sc^{3+}-\text{coloured in aqueous solution} \] \[ (III)\;Cr\text{ or }Zn-\text{higher third ionisation enthalpy} \] \[ (a)(ii)\;\text{Write the ionic equations for the oxidizing action of }MnO_4^-\text{ in acidic medium with:} \] \[ (I)\;Fe^{2+}\text{ ion} \] \[ (II)\;I^-\text{ ion} \]
Answer the following case-based questions on biomolecules: \[ (a)\;\text{Write the name of basic building units of proteins and nucleic acids. How can you differentiate between fibrous and globular proteins on the basis of their structures?} \] \[ (b)(i)\;\text{What products would be formed when a nucleotide from DNA containing thymine is hydrolyzed?} \] OR \[ (b)(ii)\;\text{Write one structural difference between DNA and RNA.} \] \[ (c)\;\text{Give one example each of a fat-soluble vitamin and a water-soluble vitamin.} \]
How will you obtain the following from benzenediazonium chloride? Give chemical equations involved: \[ (a)\;\text{Chlorobenzene} \] \[ (b)\;\text{Benzene} \] \[ (c)\;\text{Benzonitrile} \]
An organic compound \(A\) with molecular formula \(C_3H_5N\) on reaction with \(C_6H_5MgBr\) followed by hydrolysis gives compound \(B\). Compound \(B\) forms orange-red precipitate with 2,4-DNP reagent and does not give iodoform test. It neither reduces Tollens' or Fehling's reagent nor decolourises bromine water. On drastic oxidation with chromic acid it gives carboxylic acid \(C\) having molecular formula \(C_7H_6O_2\). Identify \(A\), \(B\), and \(C\). Write the reactions.
Answer the following case-based questions on alcohols, phenols and ethers: \[ (a)\;\text{Name the reagents used in the following reactions:} \] \[ (i)\;\text{Oxidation of a primary alcohol to aldehyde} \] \[ (ii)\;\text{Oxidation of a primary alcohol to carboxylic acid} \] \[ (b)\;\text{Write the reaction involved in Kolbe's reaction.} \] \[ (c)(i)\;\text{Why are tertiary alcohols resistant to oxidation?} \] OR \[ (c)(ii)\;\text{Write the products of the following reaction:} \] \[ (CH_3)_3C-O-C_2H_5 \xrightarrow{HI} \]
An antifreeze solution is prepared by dissolving \(31g\) of ethylene glycol \((M=62g\,mol^{-1})\) in \(600g\) of water. Calculate the freezing point of the solution. \[ K_f\text{ for water}=1.86K\,kg\,mol^{-1} \]
Give reasons for the following: \[ (a)\;\text{Although chlorine is an electron-withdrawing group, yet it is ortho-, para-directing in electrophilic aromatic substitution reactions.} \] \[ (b)\;\text{Aryl halides cannot be prepared by reacting phenol with concentrated halogen acids or phosphorus halides.} \] \[ (c)\;\text{Chloroform is stored in closed dark coloured bottles.} \]
Answer the following questions about the complexes \([NiCl_4]^{2-}\) and \([Ni(CN)_4]^{2-}\): \[ (i)\;\text{Write the hybridization involved in each case.} \] \[ (ii)\;\text{Which of them is the inner orbital complex and which one is the outer orbital complex?} \] \[ (iii)\;\text{Compare their magnetic behaviour.} \] \[ \text{Atomic number: }Ni=28 \]
The half-life period of a radioactive element is \(1.5\times 10^{10}\) years. Calculate the time in which the activity of the element is reduced to \(75\%\) of its original value. \[ \text{Given: }\log 2=0.30,\quad \log 3=0.48,\quad \log 4=0.60 \]
How do you explain the following? \[ (a)\;\text{Presence of a straight chain in glucose} \] \[ (b)\;\text{Presence of five }-OH\text{ groups in glucose which are attached to different carbon atoms} \]
State Kohlrausch's law of independent migration of ions. With the help of a curve, explain why it is not easy to determine \(\Lambda_m^\circ\) for weak electrolytes by extrapolating the concentration--molar conductivity curve, as it is for strong electrolytes.
Write IUPAC names of the following coordination compounds:
(i) [PtCl_2(en)_2]SO_4
(ii) (NH_4)_2[CoF_4]
For a reaction \(A+B\rightarrow\) products, the rate law is: \[ Rate=k[A][B]^{\frac{3}{2}} \] Write the overall order of the reaction. Can this reaction be an elementary reaction? Give reason.
Explain why, on addition of 1 mol of KCl to 1 litre of water, the boiling point of water increases, while addition of 1 mol of methyl alcohol to 1 litre of water decreases the boiling point.
Assertion (A): Order of reaction is applicable to elementary as well as complex reactions. Reason (R): Order of a reaction is an experimental quantity.
For the compound having molecular formula \(C_4H_9Br\), write:
(a) the isomer which is most reactive towards S_N1 displacement.
(b) the isomer which, on reacting with Na metal in dry ether, gives 2,5-dimethylhexane.
Assertion (A): Aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis. Reason (R): Gabriel phthalimide synthesis is used for the preparation of primary aliphatic amines.
On hydrolysis, which of the following carbohydrates gives only glucose?
Assertion (A): Phenol is less acidic than 4-methylphenol. Reason (R): The presence of an electron releasing group in phenol makes it less acidic.
Assertion (A): Separation of Zr and Hf is difficult. Reason (R): Because Zr and Hf lie in the same group of the periodic table.
For a reaction \(3A \rightarrow 2B\), the rate of reaction \(+\dfrac{d[B]}{dt}\) is equal to:
On electrolysis of very dilute aqueous solution of NaCl using platinum electrodes:
The mole fraction of a solute in \(2.0\) molal aqueous solution is:
The boiling point of an azeotropic mixture of water and ethanol is less than that of pure water and ethanol. The mixture shows:
Among the following, which is the strongest base?