List of top Chemistry Questions asked in CBSE CLASS XII

Assertion (A): Cuprous salts are diamagnetic.
Reason (R): In cuprous ion, 3d-orbitals are partially filled.

What amount of electric charge is required for the oxidation of 1 mole of $ \mathrm{H_2O} $ to $ \mathrm{O_2} $?

In an electrochemical cell, the following reaction takes place:
$2\mathrm{Ag^{+}(aq) + Mg(s) \rightarrow 2Ag(s) + Mg^{2+}(aq)}$
$E^{\circ}_{\mathrm{cell}} = 2.96\ \mathrm{V}$
As the reaction progresses, what will happen to the overall voltage of the cell?

(a) $E^{\circ}_{(\mathrm{Mn^{2+}/Mn})}$ is $-1.18\ \mathrm{V}$. Why is this value highly negative in comparison to neighbouring d-block elements?

(b) What is lanthanoid contraction?

(c) Zn, Cd and Hg are soft metals. Why?

Give reasons for the following observations :

(a) p-Chloronitrobenzene reacts with (aq) NaOH at 443 K to give p-nitrophenol whereas chlorobenzene reacts with the same reagent at 623 K and 300 atm.

(b) Main product obtained when chloroethane reacts with KCN is propane nitrile while with AgCN it is ethyl isocyanide.

Give reasons:

(a) Fuel cells are preferred for production of electrical energy than thermal plants.

(b) Iron does not rust even if zinc coating is broken in a galvanized pipe.

(c) In the experimental determination of electrolytic conductance, Direct Current (DC) is not used.

What is meant by the Rate law and Rate constant of a reaction. Identify the order of a reaction if the units of its Rate constant are :

(a) $ \mathrm{s^{-1}} $

(b) $ \mathrm{mol^{-1}\ L\ s^{-1}} $

Hoffmann Bromamide degradation reaction is given by:

The primary and secondary valences of Co in [Co(en)₃]Cl₃ respectively are:

The strongest base in aqueous solution among the following amines is:

The reagent that can be used to convert benzenediazonium chloride to benzene is:

Which reagents are required for one step conversion of chlorobenzene to toluene?

Which one of the following amines gives an alcohol on reaction with HNO₂?

An amine ‘X’ reacts with Hinsberg reagent and the product obtained is insoluble in alkali. The amine ‘X’ is:

Calculate $\Delta_rG^\circ$ of the following cell :

$ \mathrm{Mg(s) + Cu^{2+}(aq) \longrightarrow Mg^{2+}(aq) + Cu(s)} $

[Given : $ E^\circ_{\mathrm{Mg^{2+}/Mg}} = -2.37\ \mathrm{V} $, $ E^\circ_{\mathrm{Cu^{2+}/Cu}} = +0.34\ \mathrm{V} $, $ 1\ \mathrm{F} = 96500\ \mathrm{C\ mol^{-1}} $]

Answer the following questions:
(i) Draw structure of the methyl hemiacetal of methanal.
(ii) There are two -NH$_2$ groups in semicarbazide. However only one is involved in the formation of semicarbazones. Give reason.
(iii) How will you convert ethanol to 3-hydroxybutanal?

An organic compound (X) having molecular formula $ \mathrm{C_5H_{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.

The Crystal Field Theory (CFT) of coordination compounds is based on the effect of different crystal fields (provided by the ligands taken as point charges) on the degeneracy of d-orbital energies of the central metal atom/ion. The splitting of the d-orbitals provides different electronic arrangements in strong and weak crystal fields. In tetrahedral coordination entity formation, the d-orbital splitting is smaller as compared to the octahedral entity.
On the basis of CFT, explain why $ \mathrm{[Ti(H_2O)_6]Cl_3} $ complex is coloured ? What happens on heating the complex $ \mathrm{[Ti(H_2O)_6]Cl_3} $ ? Give reason.
[Atomic no. : Ti = 22]

Explain why electrolysis of an aqueous solution of NaCl gives $ \mathrm{H_2} $ gas at cathode and $ \mathrm{Cl_2} $ gas at anode ? Write overall reaction.
(Given : $ E^\circ_{\mathrm{Na^+/Na}} = -2.71 \ \mathrm{V} $, $ E^\circ_{\mathrm{H_2O/H_2}} = -0.83 \ \mathrm{V} $, $ E^\circ_{\mathrm{Cl_2/2Cl^-}} = +1.36 \ \mathrm{V} $, $ E^\circ_{\mathrm{H^+/O_2/H_2O}} = +1.23 \ \mathrm{V} $)

An amine 'X' reacts with Hinsberg reagent and the product obtained is soluble in alkali. The amine 'X' is:

The reaction $R$ -OH + Na $\longrightarrow$ RO$^-$ Na$^+$ + $\frac{1}{2}$ H$_2$ (g) suggests that alcohols are:

$\alpha$-D-glucose and $\beta$-D-glucose differ from each other with respect to the:

In the Arrhenius equation $ k = Ae^{-E_a/RT} $, ‘A’ represents:

We cannot measure the resistance of an ionic solution using DC because: