List of top Questions asked in CBSE CLASS XII- 2026

Equilibrium constant $\mathrm{(K_c)}$ is related to $\mathrm{E^\circ_{cell}}$, but not to $\mathrm{E_{cell}}$. Why ?
Give reasons : (I) Why does a mercury cell deliver a constant voltage for its entire life ? (II) Why is it necessary to use a salt bridge in a galvanic cell ?
The conductivity of 0·001 M acetic acid is $\mathrm{3.905\times10^{-5}}$ S $\mathrm{cm^{-1}}$. Calculate its molar conductivity and degree of dissociation $\mathrm{(\alpha)}$. [Given : $\mathrm{\lambda^\circ_{CH_3COO^-} = 40.9}$, $\mathrm{\lambda^\circ_{H^+} = 349.6\ S\,cm^2\,mol^{-1}}$]
Arrange the following compounds in increasing order of their reactivity towards HCN : $\mathrm{CH_3COCH_3,\ CH_3CHO,\ (CH_3)_3C\text{-}CO\text{-}CH_3}$.
Write the reaction involved in the Etard reaction.
Write the product when
reacts with Zn(Hg)/conc. HCl.
Draw / write the structure of the semicarbazone of acetone.
Why are $\mathrm{\alpha}$-hydrogen atoms of aldehydes and ketones acidic in nature ?
Write the product(s) of the following :
(I) One mol of ethanal is treated with 1 mol of $\mathrm{CH_3OH}$ in the presence of dry HCl gas.
(II) Benzaldehyde is treated with conc. NaOH.
(III) Ethanoic acid is heated in the presence of $\mathrm{P_2O_5}$.
Write a simple chemical test to distinguish between Ethanal and Propanal.
Write the name of the reagent to transform Allyl alcohol to Propanal.
Give reasons for the following :
(a) Haloalkanes react with KCN to form alkyl cyanides, while with AgCN they form isocyanides.
(b)
is more reactive towards $\mathrm{S_N2}$ displacement as compared to
.
(c) Grignard reagents should be prepared under anhydrous conditions.
The half-life period of a radioactive element is $\mathrm{1.5\times10^{10}}$ years. Calculate the time in which the activity of the element is reduced to 75% of its original value. [Given : log 2 = 0·30, log 3 = 0·48, log 4 = 0·60]
Name two coordination compounds which are important in biological systems.
How will you obtain the following from aniline ? Write the chemical equations involved :
(a) Sulphanilic acid
(b) 2,4,6-Tribromoaniline
(c) Acetanilide
An organic compound (A) with molecular formula $\mathrm{C_3H_5N}$ on reaction with $\mathrm{C_6H_5MgBr}$ followed by hydrolysis, gives a compound (B). Compound (B) forms an orange-red precipitate with 2,4-DNP reagent and does not give iodoform test. It neither reduces Tollens' or Fehling's reagent nor does it decolourise bromine water. On drastic oxidation with chromic acid it gives a carboxylic acid (C) having molecular formula $\mathrm{C_7H_6O_2}$. Identify the compounds (A), (B) and (C). Write the reactions of compound (A) with $\mathrm{C_6H_5MgBr}$ followed by hydrolysis to give compound (B).
What is meant by chelate effect ? Give an example.
Why are low spin tetrahedral complexes rarely formed ?
An antifreeze solution is prepared by dissolving 31 g of ethylene glycol (Molar mass = 62 g $\mathrm{mol^{-1}}$) in 600 g of water. Calculate the freezing point of the solution. ($\mathrm{K_f}$ for water = 1·86 K kg $\mathrm{mol^{-1}}$)
How do you explain the following ?
(a) Presence of an aldehyde group in glucose
(b) Presence of a primary alcoholic group in glucose
Explain why, on addition of 1 mol of KCl to 1 litre of water, the boiling point of water increases, while the addition of 1 mol of methyl alcohol to 1 litre of water decreases the boiling point.
Answer the following questions about the complexes $\mathrm{[NiCl_4]^{2-}}$ and $\mathrm{[Ni(CN)_4]^{2-}}$ :
(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 : Ni = 28]
State Kohlrausch's law of independent migration of ions. With the help of a curve, explain why it is not easy to determine $\mathrm{\Lambda^\circ_m}$ for weak electrolytes by extrapolating the concentration – molar conductivity curve, as it is for strong electrolytes.
Write IUPAC names of the following compounds :
(i) $\mathrm{[PtCl_2(en)_2]SO_4}$
(ii) $\mathrm{(NH_4)_2[CoF_4]}$
For a reaction A + B → Products, the rate law is $\mathrm{Rate = k[A][B]^{3/2}}$. Write the overall order of the reaction. Can this reaction be an elementary reaction ? Give reason in support of your answer.