List of top Questions asked in CBSE CLASS XII- 2026

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 ?
Write the products of the following reaction : \[ (CH_3)_3C-O-C_2H_5 \xrightarrow{HI} ? \]
Why are tertiary alcohols resistant to oxidation ?
Write the reaction involved in Kolbe's reaction.
Name the reagents used in the following reactions : (i) Oxidation of a primary alcohol to aldehyde (ii) Oxidation of a primary alcohol to carboxylic acid
Name two coordination compounds which are important in biological systems. (ii) What is meant by chelate effect ? Give an example. (iii) Why are low spin tetrahedral complexes rarely formed ?
Answer the following questions about the complexes \[ [NiCl_4]^{2-} \quad \text{and} \quad [Ni(CN)_4]^{2-} \] (i) Write the hybridization involved in each case. (ii) Which of them is the inner orbital complex and which one is the outer orbital complex ? (iii) Compare their magnetic behaviour. (Atomic Number of Ni = 28)
Why does a mercury cell deliver a constant voltage for its entire life?
Why is it necessary to use salt bridge in a galvanic cell?
Why are low spin tetrahedral complexes rarely formed?
\[ \text{What happens when an acidic solution of the green compound }(B)\text{ is allowed to stand for some time? Also write the equation involved. What is this type of reaction called?} \]
\[ \text{Why are }\alpha\text{-hydrogen atoms of aldehydes and ketones acidic in nature?} \]
\[ \text{Arrange the following compounds in increasing order of their reactivity towards }HCN: \]
\[ CH_3COCH_3,\quad CH_3CHO,\quad (CH_3)_3C-CO-CH_3 \]
Write the reaction involved in Etard reaction.
\[ \text{Write the product when cyclohexanecarbaldehyde reacts with }Zn(Hg)/conc.\;HCl. \]
Give reasons for the following:
What is meant by chelate effect? Give an example.
Define Double Salt with one example.
\[ \text{The conductivity of }0.001M\text{ solution of acetic acid is }3.905\times10^{-5}\;S\,cm^{-1}.\text{ Calculate its molar conductivity and degree of dissociation }(\alpha). \]
\[ \lambda^\circ_{CH_3COO^-}=40.9\;S\,cm^2mol^{-1} \]
\[ \lambda^\circ_{H^+}=349.6\;S\,cm^2mol^{-1} \]
Draw the structure of the semicarbazone of acetone.
\[ \text{A black-brown coloured solid }(A)\text{ when fused with }KOH\text{ in the presence of air, produces a dark green compound }(B)\text{ which on electrolytic oxidation in alkaline medium gives a dark purple coloured compound }(C).\text{ Identify }(A),(B)\text{ and }(C).\text{ Write the reactions involved.} \]
Name two coordination compounds which are important in biological systems.
Define Ambidentate Ligand with one example.
The rate of the chemical reaction doubles when the temperature is raised from \(298\,K\) to \(308\,K\). Calculate activation energy \((E_a)\) for this reaction assuming that it does not change with temperature. (Given : \(R = 8.314\,J\,mol^{-1}\,K^{-1}\), \(\log 2 = 0.30\))
Calculate emf of the following cell at \(298\,K\) : \[ Cr(s)\,|\,Cr^{3+}(aq,\;0.1\,M)\,||\,Fe^{2+}(aq,\;0.01\,M)\,|\,Fe(s) \] (Given : \[ E^\circ_{Cr^{3+}/Cr}=-0.74\,V, \] \[ E^\circ_{Fe^{2+}/Fe}=-0.44\,V, \] \[ \log 10 = 1 \] )