List of top Chemistry Questions asked in CBSE CLASS XII

Assertion (A): Electrolysis of aqueous NaCl gives H$_2$ at cathode and Cl$_2$ at anode.
Reason (R): Chlorine has higher oxidation potential than H$_2$O.

Hoffmann Bromamide degradation reaction is given by:

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

Out of the following statements, the incorrect statement is:

The value of Henry's constant K$_H$ is:

In the Haworth structure of the following carbohydrate, various carbon atoms have been numbered. The anomeric carbon is numbered as:

Out of 2-Bromobutane, 1-Bromobutane, 2-Bromopropane and 1-Bromopropane, the molecule which is chiral in nature is:

Out of Fe$^{3+}$, Sc$^{3+}$, Cr$^{3+}$ and Co$^{3+}$ ions, the one which is colourless in aqueous solution is:

In an electrochemical cell, the following reaction takes place : $2\text{Cu}^{2+} (\text{aq}) + \text{Zn} (\text{s}) \rightarrow 2\text{Cu} (\text{s}) + \text{Zn}^{2+} (\text{aq})$
$E^\circ_{\text{cell}} = 1.28 \, \text{V}$
As the reaction progresses, what will happen to the overall voltage of the cell?

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

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

Out of Fe$^{3+}$, Sc$^{3+}$, Cr$^{3+}$ and Co$^{3+}$ ions, the one which is colourless in aqueous solution is:

What amount of electric charge is required for the reduction of 1 mole of MnO$_4^{2-}$ into Mn$^{2+}$?

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

Give reasons:
(I) $[ \text{Ni(CO)}_4 ]$ is diamagnetic whereas $[ \text{NiCl}_4 ]^{2-}$ is paramagnetic. [Atomic number: Ni = 28]
(II) CO is a stronger complexing agent than NH$_3$.
(III) The trans isomer of complex $[ \text{Co(en)}_2\text{Cl}_2 ]^{+}$ is optically inactive.

Complete each synthesis by giving missing starting material, reagent, or products: (I) $\text{CH}_3\text{CH}_3 + \text{KMnO}_4, \text{KOH} \longrightarrow \text{?}$

(i) The initial concentration of N$_2$O$_5$ in the first-order reaction:
\[ \text{N}_2\text{O}_5 (\text{g}) \rightarrow 2 \text{NO}_2 (\text{g}) + \frac{1}{2} \text{O}_2 (\text{g}) \] was $ 1.2 \times 10^{-2} $ mol L$^{-1}$. The concentration of N$_2$O$_5$ after 60 minutes was $ 0.2 \times 10^{-2} $ mol L$^{-1}$. Calculate the rate constant of the reaction at 318 K.
$[ \log 6 = 0.778 ]$

(ii) Account for the following:
(I) We cannot determine the order of a reaction by taking into consideration the balanced chemical equation.
(II) A bimolecular reaction may become kinetically first order under a specified condition.

According to the generally accepted definition of the ideal solution there are equal interaction forces acting between molecules belonging to the same or different species. (This is equivalent to the statement that the activity of the components equals the concentration.) Strictly speaking, this concept is valid in ecological systems (isotopic mixtures of an element, hydrocarbons mixtures, etc.). It is still usual to talk about ideal solutions as limiting cases in reality since very dilute solutions behave ideally with respect to the solvent. This law is further supported by the fact that Raoult’s law empirically found for describing the behaviour of the solvent in dilute solutions can be deduced thermodynamically via the assumption of ideal behaviour of the solvent.
Answer the following questions:
(a) Give one example of miscible liquid pair which shows negative deviation from Raoult’s law. What is the reason for such deviation?
(b) (i) State Raoult’s law for a solution containing volatile components.
OR
(ii) Raoult’s law is a special case of Henry’s law. Comment.
(c) Write two characteristics of an ideal solution.

(ii) Carry out the following conversions: (I) Benzaldehyde to Benzophenone

Ribose and 2-deoxyribose have an important role in biology. Among the most important derivatives are those with phosphate groups attached at the 5 position. Mono-, di- and tri-phosphate forms are important, as well as 3-5 cyclic monophosphates. Purines and pyrimidines form an important class of compounds with ribose and deoxyribose. When these purine and pyrimidine derivatives are coupled to a ribose sugar, they are called nucleosides.
Answer the following questions :
(a) What products would be formed when DNA is hydrolyzed? How is DNA different from RNA with reference to structure?