List of top Chemistry Questions asked in CBSE CLASS XII

What happens when:
(I) The manganate ion undergoes disproportionation reaction in acidic medium?
(II) KMnO4 is heated?

Calculate the \(E^\circ_{{Mg^{2+}/Mg}}\) potential for the following half-cell at 25°C:
Mg/Mg2+(1 × 10−4 M), E0 Mg2+/Mg = +2.36 V

State Faraday’s first law of electrolysis. How much electricity, in terms of Faraday, is required to reduce one mole of MnO4− to Mn2+ ion?
The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1000 ohm. What is the cell constant if conductivity of 0.001 M KCl solution at 298 K is 0.125 × 10−3 S cm−1?
Why does Vanadium pentoxide (V2O5) act as a catalyst?
How will you obtain the following from aniline? Give chemical equations only.
(a)Sulphanilic acid
(b) Phenylisocyanide
(c) Acetanilide
Give reasons for the following:
(a)The pH of aqueous NaCl increases when it is electrolyzed.
(b) Unlike dry cell, mercury cell has a constant cell potential through its lifetime.
(c) Conductivity of solution decreases with dilution.

Answer the following:
(i) What happens to the colour of the complex \([ \text{Ti(H}_2\text{O)}_6 ]^{3+}\) when heated gradually?
(ii) Write the electronic configuration for a \(d^5\) ion if \(\Delta_o < P\).
(iii) Write the hybridization and magnetic behaviour of the complex \([ \text{Ni(CO)}_4 ]\).
(Atomic number: Ni = 28)

A compound (A) with molecular formula C\(_4\)H\(_9\)N on reduction with DIBAL-H followed by hydrolysis, gives a compound (B). Compound (B) gives positive Tollens’ test but does not give iodoform test. Compound (B) can also be obtained when ethanal is treated with dilute NaOH followed by heating. Identify (A) and (B). Write the reactions of (A) with DIBAL-H followed by hydrolysis.
Answer the following about the complexes \([ \text{FeF}_6]^{3-} \text{ and } [\text{Fe(CN)}_6]^{4-}\):
(i) Write the hybridization involved in each case.
(ii) Which of them is the outer orbital complex and which one is the inner orbital complex?
(iii) Compare their magnetic behaviour.
[Atomic number: Fe = 26]
Vapour pressure of pure water at 298 K is 24.8 mm Hg. Calculate the lowering in vapour pressure of an aqueous solution which freezes at –0.3°C. (K\(_f\) of water = 1.86 K kg mol\(^{-1}\))

The rate of a reaction:
A + B −→ 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\(^{-1}\))
10.010.01\(5 \times 10^{-3}\)
20.020.01\(1 \times 10^{-2}\)
30.010.02\(5 \times 10^{-3}\)
State Henry's law. Why are aquatic species more comfortable in cold water as compared to warm water?
Differentiate between:
(i) Double salt and Complex compound
(ii) Didentate ligand and Ambidentate ligand
Assertion (A): Phenol is strongly acidic as compared to ethanol.
Reason (R): Phenoxide ion is more stable than ethoxide ion.
Write IUPAC names of the following coordination compounds:
\([ \text{CoCl}_2(\text{en})_2]\text{SO}_4 \)
(ii) \( \text{K}_3[\text{Fe}(\text{C}_2\text{O}_4)_3] \)
(ii) Didentate ligand and Ambidentate ligand
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 do you explain the following?
(a) Presence of an aldehyde group in glucose.
(b) Presence of five –OH groups in glucose.
Draw the structures of major monohalo products in each of the following reactions:
methylbenzene (CH3C6H5)

\( \text{CH}_3\text{C}_6\text{H}_5 + \text{HI} \longrightarrow \) ?
(b) \( \text{C}_6\text{H}_6 + \text{Br}_2 \longrightarrow \) Heat or UV light ?
Pyranose ring of glucose is formed due to the reaction between:
Assertion (A): Hydrolysis of an ester follows first order kinetics.
Reason (R): The concentration of water does not get altered much during the reaction.
Which of the following cell converts the energy of combustion of fuel into electrical energy?
The unit of rate and rate constant are the same for a:
Assertion (A): Actinoids show wide range of oxidation states.
Reason (R): Actinoids are radioactive in nature.
Assertion (A): Boiling point of (CH₃)₃N is higher than that of CH₃CH₂CH₂NH₂.
Reason (R): Hydrogen bonding is more extensive in CH₃CH₂CH₂NH₂.