List of top Questions asked in CBSE CLASS XII- 2025

Calculate the \( E_{Mg^{2+}/Mg} \) potential for the following half cell at 25°C :

Mg/Mg²⁺(1 × 10⁻⁴ M); E°_Mg²⁺/Mg = +2.36 V

[Given : log 10 = 1]

The rate of a reaction:
A + B \(\to\) product
is given below as a function of different initial concentrations of A and B.

Experiment	\([A]\) / mol L\(^{-1}\)	\([B]\) / mol L\(^{-1}\)	Initial Rate / mol L\(^{-1}\) min\(^{-1}\)
1	0.01	0.01	\(5 \times 10^{-3}\)
2	0.02	0.01	\(1 \times 10^{-2}\)
3	0.01	0.02	\(5 \times 10^{-3}\)

Calculate the order of the reaction with respect to A and B. Determine the rate constant of the reaction.

Identify P, Q and R in the following reaction sequence:
\[ P \xrightarrow{\mathrm{NH_3}} \mathrm{CH_3COO^-NH_4^+} \xrightarrow{\Delta} Q \]
\[ P \xrightarrow{\mathrm{PCl_5}} R \]

When pyrolusite ore is fused with KOH, in presence of air, a dark green coloured product 'A' is obtained which changes to purple coloured compound 'B' in acidic medium.
(I) Write the formulae of 'A' and 'B'.
(II) Write the ionic equation for the reaction when compound 'B' reacts with Fe²⁺ in acidic medium.

Match the type of cell given in Column I with their use given in Column II.

Column I	Column II
i. Lead storage cell	a. Wall clock
ii. Mercury cell	b. Apollo Space Programme
iii. Dry cell	c. Wrist watch
iv. Fuel cell	d. Inverter

In which of the following groups are both ions coloured in aqueous solution?
I. \( Cu^{+} \) II. \( Ti^{4+} \) III. \( Co^{2+} \) IV. \( Fe^{2+} \)
[Atomic number : Cu = 29, Ti = 22, Co = 27, Fe = 26]

Which of the following aldehydes will undergo Cannizzaro reaction?

Out of \( \mathrm{Ti^{3+}} \), \( \mathrm{Cr^{3+}} \), \( \mathrm{Fe^{2+}} \) and \( \mathrm{Ni^{2+}} \) ions, the one which is the most stable ion in aqueous solution is:

[Atomic number : Ti = 22, Cr = 24, Fe = 26, Ni = 28]

Complete each synthesis by giving missing starting material, reagent or products:
(I) Ethylbenzene \(\xrightarrow{\text{(i) KMnO}_4,\ \text{KOH};\ \text{(ii) H}_3\text{O}^{+}}\ ?\)
(II) Methylenecyclohexane \(\xrightarrow{\ ?\ }\) Cyclohexanecarbaldehyde
(III) 4-Oxocyclohexane-1-carbaldehyde \(\xrightarrow{[\text{Ag(NH}_3)_2]^{+}}\ ?\)

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 condition is fulfilled only in exceptional cases for mixtures (optical isomers, isotopic mixtures of an element, hydrocarbon mixtures). 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 view 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.

An aqueous solution of NaOH was made and its molar mass from the measurement of osmotic pressure at 27°C was found to be 25 g mol\(^{-1}\). Calculate the percentage dissociation of NaOH in this solution.
[Atomic mass : Na = 23 u, O = 16 u, H = 1 u]

Calculate the cell voltage of the voltaic cell which is set up by joining following half-cells at 25°C:
Al/Al³⁺ (0.001 M) and Ni/Ni²⁺ (0.1 M)
Given : \( E^\circ_{\mathrm{Ni^{2+}/Ni}} = -0.25 \) V, \( E^\circ_{\mathrm{Al^{3+}/Al}} = -1.66 \) V

Complete the following reactions by writing the structural formulae of 'A' and 'B':

(i) \( \mathrm{CH_3CH=CH_2} \xrightarrow[\text{Peroxide}]{\text{HBr}} \) 'A' \( \xrightarrow{\text{aq. KOH}} \) 'B'

(ii) \( \mathrm{CH_3CH_2CH(Cl)CH_3} \xrightarrow[\Delta]{\text{alc. KOH}} \) 'A' \( \xrightarrow{\text{HBr}} \) 'B'

(iii) 'A' \( \xrightarrow{\text{Mg}} \mathrm{CH_3CH_2MgCl} \xrightarrow[\mathrm{H^+}]{\mathrm{H_2O}} \) 'B' (Main product)

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

[Atomic number : Fe = 26, Sc = 21, Cr = 24, Co = 27]

Out of Ti³⁺, Cr³⁺, Mn²⁺ and Ni²⁺ ions, the one which has the highest magnetic moment is:
[Atomic number : Ti = 22, Cr = 24, Mn = 25, Ni = 28]

Assertion (A): Henry’s law constant (KH) decreases with increase in temperature.
Reason (R): As the temperature increases, solubility of gases in liquids decreases.

Write IUPAC names of the following :

(i) \( [\mathrm{Co(H_2O)(CN)(en)_2}]^{2+} \)

(ii) \( [\mathrm{PtCl_4}]^{2-} \)

(iii) \( [\mathrm{Cr(NH_3)_4Cl(ONO)}]^{+} \)

In the following complex ion, explain the type of hybridisation, shape and magnetic property :

\(\mathrm{[Fe(H_2O)_6]^{2+}}\)

(At. Nos. : Fe = 26, Ni = 28)

Henry's law constant for \(\mathrm{CO_2}\) in water is \(1.67 \times 10^{8}\) Pa at 298 K. Calculate the number of moles of \(\mathrm{CO_2}\) in 500 ml of soda water when packed under \(2.53 \times 10^{5}\) Pa at the same temperature.

Calculate \(\Delta_r G^{\circ}\) and \(\log K_C\) of the reaction.

\(\mathrm{2Cr(s) + 3Cd^{2+}(aq) \to 2Cr^{3+}(aq) + 3Cd(s)}\)

Given \(E^{\circ}_{\mathrm{Cr^{3+}/Cr}} = -0.74\) V, \(E^{\circ}_{\mathrm{Cd^{2+}/Cd}} = -0.40\) V

[R = 8.314 J \(\mathrm{K^{-1}\,mol^{-1}}\), F = 96500 C \(\mathrm{mol^{-1}}\)]