List of top Chemistry Questions asked in CBSE CLASS XII

The vapour pressures of A and B at 25°C are 75 mm Hg and 25 mm Hg, respectively. If A and B are mixed such that the mole fraction of A in the mixture is 0.4, then calculate the mole fraction of B in the vapour phase.
A 6% solution of glucose (molar mass = 180 g mol\(^{-1}\)) is isotonic with a 2.5% solution of an unknown organic substance. Calculate the molecular weight of the unknown organic substance.
The vapour pressures of A and B at 25°C are 75 mm Hg and 25 mm Hg, respectively. If A and B are mixed such that the mole fraction of A in the mixture is 0.4, then calculate the mole fraction of B in the vapour phase.
Which of the following compounds will give a ketone on oxidation with chromic anhydride (CrO3})?
Draw the structures of major monohalo products in each of the following reactions: 
structures of major monohalo products

(b) Give reasons for the following:
(i) Grignard reagent should be prepared under anhydrous conditions.
(ii) Alkyl halides give alcohol with aqueous KOH whereas in the presence of alcoholic KOH, alkenes are formed
The product (X) obtained in the following reaction is:
product (X) obtained
Phenol does not undergo nucleophilic substitution reaction easily due to:
Assertion (A): \( p \)-nitroaniline is a weaker base than \( p \)-toluidine.
Reason (R): The electron-donating \( -NO_2 \) group in \( p \)-nitroaniline makes it a weaker base.
Assertion (A): \( \Delta_{\text{mix}} H \) for an ideal solution is not equal to zero.
Reason (R): A–B interactions in an ideal solution are the same as between A–A and B–B interactions.
Write the chemical equations when:
(a) Ethanal is treated with 2,4-dinitrophenylhydrazine?
(b) Propanone is treated with Zn(Hg) and conc. HCl?
For a chemical reaction \( R \to P \), the variation in the concentration \([R]\) vs time \( t \) plot is given as:
variation in the concentration

(a) Predict the order of the reaction and write the unit of rate constant (\( k \)) for this order of reaction.
(b) What is the slope of the curve?
All proteins on hydrolysis give:
The suitable Grignard reagent used for the synthesis of
Grignard reagent

with methanal is:
Assertion (A): Fluoroacetic acid is a stronger acid than chloroacetic acid. Reason (R): This is due to greater electron-withdrawing nature of \( F \) than \( Cl \).
Which of the following has the highest boiling point?
A zero-order reaction is one whose rate is independent of:
Which of the following is most reactive towards nucleophilic substitution reaction?
In the Arrhenius equation, when \( \log k \) is plotted against \( 1/T \), a straight line is obtained whose:
Maltose is made up of:
Which of the following is the strongest acid?
The system that forms maximum boiling azeotrope is:
The equilibrium \( \text{Cr}_2\text{O}_7^{2-} \rightleftharpoons 2\text{CrO}_4^{2-} \):
The following initial rate data were obtained for the reaction: \[ 2\text{NO (g)} + \text{Br}_2 \text{(g)} \rightarrow 2 \text{NOBr (g)} \] initial rate data were obtained for the reaction
Write the chemical equation when:
(a) Butan-2-one is treated with Zn(Hg) and conc. HCl.
(b) Two molecules of benzaldehyde are treated with conc. NaOH.
Define colligative property. Which colligative property is preferred for the molar mass determination of macromolecules?