List of top Chemistry Questions asked in CBSE CLASS XII

Assertion (A): Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis. Reason (R): Aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide.

Assertion (A): Vitamin D cannot be stored in our body. Reason (R): Vitamin D is fat-soluble vitamin and is not excreted from the body in urine.

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

Read the passage carefully and answer the questions that follow.
Passage: The rate of a chemical reaction is expressed either in terms of decrease in the concentration of reactants or increase in the concentration of a product per unit time. Rate of the reaction depends upon the nature of reactants, concentration of reactants, temperature, presence of catalyst, surface area of the reactants and presence of light. Rate of reaction is directly related to the concentration of reactant. Rate law states that the rate of reaction depends upon the concentration terms on which the rate of reaction actually depends, as observed experimentally. The sum of powers of the concentration of the reactants in the Rate law expression is called order of reaction while the number of reacting species taking part in an elementary reaction which must collide simultaneously in order to bring about a chemical reaction is called molecularity of the reaction.
 Answer the following questions:

Phenols undergo electrophilic substitution reactions readily due to the strong activating effect of the OH group attached to the benzene ring. Since the OH group increases the electron density more to the ortho- and para- positions, one of the examples of the aldehyde group being introduced on the aromatic ring of phenol, ortho to the hydroxyl group. This is a general method used for the ortho-formylation of phenols.
Answer the following questions:

How many Faradays are required for the oxidation of one mole of \( \text{H}_2\text{O} \) to \( \text{O}_2 \)?

The vapour pressures of A and B at 25°C are 75 mm Hg and 25 mm Hg, respectively. If A and B are mixed such that the mole fraction of A in the mixture is 0.4, then calculate the mole fraction of B in the vapour phase.

The melting and boiling points of Zn, Cd, and Hg are low.

When a certain conductivity cell was filled with 0.05 M KCl solution, it has a resistance of 100 ohms at 25°C. When the same cell was filled with 0.02 M AgNO3 solution, the resistance was 90 ohms. Calculate the conductivity and molar conductivity of $\text{AgNO}_{3}$ solution.
Given: Conductivity of 0.05 M KCl solution = \( 1.35 \times 10^{-2} \, \Omega^{-1} \, \text{cm}^{-1} \)

The vapour pressure of a solvent at 283 K is 100 mm Hg. Calculate the vapour pressure of a dilute solution containing 1 mole of a strong electrolyte AB in 50 moles of the solvent at 283 K (assuming complete dissociation of solute AB).

Which isomer of C₄H₉Cl has the lowest boiling point?

The resistance of 0.05 M CH\(_3\)COOH solution is found to be 100 ohm. If the cell constant is 0.0354 cm\(^{-1}\), calculate the molar conductivity of the acetic acid solution.

Write the stepwise mechanism of nucleophilic addition reactions in the carbonyl compounds.

An amide ‘A’ with molecular formula C$_7$H$_7$ON undergoes Hoffmann Bromamide degradation reaction to give amine ‘B’. ‘B’ on treatment with nitrous acid at 273-278 K forms ‘C’ and on treatment with chloroform and ethanolic potassium hydroxide forms ‘D’. ‘C’ on treatment with ethanol gives ‘E’. Identify ‘A’, ‘B’, ‘C’, ‘D’ and ‘E’ and write the sequence of chemical equations.