List of top Chemistry Questions asked in CBSE CLASS XII

Assertion (A): Rate of reaction decreases with increase in temperature. Reason (R): Number of effective collisions increases with increase in temperature.

CH$_3$-O-CH$_3$ when treated with excess HI gives:

‘Scurvy’ is caused by the deficiency of vitamin:

Which of the following elements of the 3d series of transition elements has the lowest $\Delta_{a} H^\circ$?

Consider the following reaction:

The major product obtained is:

On adding AgNO$_3$ solution to 1 mole of CoCl$_3$·4NH$_3$, one mole of AgCl is precipitated. The secondary valency of Co is:

Which of the following ligands is an ambidentate ligand?

Carbohydrates are the major components of all living organisms. Sugars are carbohydrates. The major types of sugars include monosaccharides and disaccharides. The main difference between monosaccharides, disaccharides and polysaccharides is that monosaccharides are monomer of sugars and disaccharides are composed of two monomers, whereas polysaccharides are composed of a large number of monomers. Monosaccharides are single sugar molecules which act as the building blocks of disaccharides and polysaccharides. Disaccharides are also simple sugars. Disaccharides are classified into two groups according to their reducing strength: Reducing and Non-reducing sugars. When a polymer is formed from a monomer, a condensation reaction occurs that forms a glycosidic bond and water molecule is lost. Starch, glycogen and cellulose are examples of polysaccharides. Starch is found in many parts of plant cell and consists of amylose and amylopectin. Glycogen is the major carbohydrate storage product found in humans. It is present in liver, muscles and brain.

Cellulose is the most abundant organic molecule on Earth. It makes up around 50% of all organic carbon.

Raoult’s law for volatile liquids states that the partial vapour pressure of each component in the solution is directly proportional to its mole fraction, whereas for a non-volatile solute, it states that the vapour pressure of a solution of a non-volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied by its mole fraction.

Two liquids A and B are mixed with each other to form a solution, the vapour phase consists of both components of the solution. Once the components in the solution have reached equilibrium, the total vapour pressure of the solution can be determined by combining Raoult’s law with Dalton’s law of partial pressures.

If a non-volatile solute B is dissolved into a solvent A to form a solution, the vapour pressure of the solution will be lower than that of the pure solvent.

The solutions which obey Raoult’s law over the entire range of concentration are ideal solutions, whereas the solutions for which vapour pressure is either higher or lower than that predicted by Raoult’s law are called non-ideal solutions.

Non-ideal solutions are identified by determining the strength of the intermolecular forces between the different molecules in that particular solution. They can either show positive or negative deviation from Raoult’s law depending on whether the A – B interactions in solution are stronger or weaker than A – A and B – B interactions.

Compound A undergoes Rosenmund reduction to give compound B with molecular formula $C_7$H₆O. Compound B does not give Fehling’s test but reacts with conc. NaOH to give C and D.
Identify A, B, C and D and write all the reactions involved.
Write one chemical test to distinguish between compound B and propanone.

Why do transition metals form large numbers of complex compounds?

How does acidified potassium permanganate solution react with $Fe^{2+}$ ions? Write ionic equation.

Calculate the ‘spin only’ magnetic moment of a divalent ion of a metal M in aqueous solution. The atomic number of the metal M is 25.

Calculate emf of the given cell: Mg(s) $\mid$ Mg$^{2+}$(0.1 M) $\parallel$ Cu$^{2+}$(1.0 × 10$^{-3}$ M) $\mid$ Cu(s)
Given:
$E^\circ_{\text{Cu}^{2+}/\text{Cu}} = +0.34$ V, \quad $E^\circ_{\text{Mg}^{2+}/\text{Mg}} = -2.37$ V
(log 100 = 2)

State Kohlrausch’s law of independent migration of ions.

How much electricity in terms of Faraday is required to produce 40 g of Al from molten Al$_2$O$_3$? (Given: Atomic mass of Al = 27 u)

Calculate log $K_c$ for the following reaction at 298 K: Zn(s) + Cu$^{2+}$(aq) $\rightleftharpoons$ Zn$^{2+}$(aq) + Cu(s)
Given:
$E^\circ_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V}$, \quad $E^\circ_{\text{Cu}^{2+}/\text{Cu}} = +0.34 \, \text{V}$

Compound A with molecular formula (C₂H₆O) on oxidation by PCC gives compound B, which on treatment with dilute alkali forms compound C (a β-hydroxy aldehyde). B on oxidation by potassium permanganate forms C.
Identify A, B, C and D and write all the chemical equations involved.

The chemistry of the actinoids is more complex as compared to the lanthanoids. Why?

Why is E for Mn³⁺/Mn²⁺ redox couple more positive?