List of top Chemistry Questions asked in CBSE CLASS XII

The reaction between H$_2$ (g) and I$_2$ (g) was carried out in a sealed isothermal chamber. The rate law for the reaction was found to be: \[ \text{Rate} = k[\text{H}_2][\text{I}_2] \] If 1 mole of H$_2$ (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.

Why does Vanadium pentoxide (V2O5) act as a catalyst?

The elements of the 3d transition series are given as: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. Answer the following:

Copper has an exceptionally positive $ E^\circ_{\text{M}^{2+}/\text{M}} $ value, why?

A certain reaction is 50 complete in 20 minutes at 300 K and the same reaction is 50 complete in 5 minutes at 350 K. Calculate the activation energy if it is a first order reaction.
Given: \[ R = 8.314 \, \text{J K}^{-1} \, \text{mol}^{-1}, \quad \log 4 = 0.602 \]

Which of the following molecules is chiral in nature?

Why is a solution of Ni(H₂O)₆²⁺ green while a solution of Ni(CN)₄²⁻ is colourless? (At. No. of Ni = 28)

Observe the graph in the given figure and answer the following questions:

linear relationship between log |R0| and time.

(a) Predict the order of reaction.
(b) What is the slope of the curve?

How can you obtain the following?
(a) Aniline from ammonium benzoate
(b) Benzene diazonium chloride from nitrobenzene
(c) 2,4,6-Tribromoaniline from aniline

Assertion (A): In a first order reaction, if the concentration of the reactant is doubled, its half-life is also doubled.
Reason (R): The half-life of a reaction does not depend upon the initial concentration of the reactant in a first order reaction.

The value of rate constant for a pseudo first order reaction:

In the following pair of halogen compounds, which compound undergoes $ S_N1 $ reaction faster and why?

Write the reactions involved when D-glucose is treated with the following reagents:
(a) HCN
(b) Br$_2$ water

Complete the following reactions by writing the structure of the main products:

Which is the correct order of acid strength from the following?

In case of association, abnormal molar mass of solute will:

While doing qualitative analysis in chemistry lab, Abhishek added yellow coloured potassium chromate solution into a test tube. He was surprised to see the colour of the solution changing immediately to orange. He realised that the test tube was not clean and contained a few drops of some liquid. Which of the following substances will be the most likely liquid to be present in the test tube before adding potassium chromate solution?

Among the following outermost electronic configurations of transition metals, which one shows the highest oxidation state?

Arrange the following compounds in increasing order of their boiling point:
\[ \text{(CH}_3\text{)}_2\text{NH, CH}_3\text{CH}_2\text{NH}_2, \text{CH}_3\text{CH}_2\text{OH} \]

Tertiary alkyl halides are least reactive towards SN2 reaction.

PCl$_3$, 2KCl does not give precipitate of AgCl with AgNO$_3$ solution. Write the structural formula and IUPAC name of the complex.

An organic compound (X) having molecular formula C$_5$H$_10$O can show various properties depending on its structures. Draw each of the structures if it:
(I) shows Cannizzaro reaction.
(II) reduces Tollens' reagent and has a chiral carbon.
(III) gives positive iodoform test.

In the given reaction sequence, the structure of Y would be:

Assertion (A): Molecularity of reaction is determined experimentally. Reason (R): Molecularity is applicable only for an elementary reaction and not for a complex reaction.

Assertion (A): The boiling points of alkyl halides decrease in the order: RI > RBr > RCl > RF.
Reason (R): The boiling points of alkyl chlorides, bromides and iodides are considerably higher than that of the hydrocarbon of comparable molecular mass.

(A) Explain the following reactions and write chemical equations involved:
(a) Wolff-Kishner reduction
(b) Etard reaction
(c) Cannizzaro reaction