List of top Chemistry Questions asked in CBSE CLASS XII

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.

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.

An alkene A with molecular formula C\(_6\)H\(_{10}\) on ozonolysis gives a mixture of two compounds B and C. Compound B gives positive Fehling test and also reacts with iodine and NaOH solution. Compound C does not give Fehling solution test but forms iodoform. Identify the compounds A, B, and C.

Using \( E^\circ \) values of X and Y given below, predict which is better for coating the surface of iron to prevent corrosion and why?
Given: \( E^\circ_{X^{2+}/X} = -2.36 \, \text{V} \) \( E^\circ_{Y^{2+}/Y} = -0.14 \, \text{V} \) \( E^\circ_{Fe^{2+}/Fe} = -0.44 \, \text{V} \)

Define Azeotrope. What type of Azeotrope is formed by negative deviation from Raoult's law? Give an example.

The correct IUPAC name of [Pt(NH$_3$)$_2$Cl$_2$]$^{2+} $ is:

The magnetic moment is associated with its spin angular momentum and orbital angular momentum. Spin only magnetic moment value of Cr$^{3+}$ ion (Atomic no. : Cr = 24) is:

Standard electrode potential for Sn$^{4+}$/Sn$^{2+}$ couple is +0.15 V and that for the Cr$^{3+}$/Cr couple is -0.74 V. The two couples in their standard states are connected to make a cell. The cell potential will be:

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:

Carry out the following conversion
Propanoic acid to Ethane

What type of isomerism is shown by the complex [Co(NH₃)₆][Cr(CN)₆]?

Carry out the following conversion
Ethanal to But-2-enal

Answer the following:
Low spin tetrahedral complexes are not known.

Why is a solution of Ni(H₂O)₆²⁺ green while a solution of Ni(CN)₄²⁻ is colourless? (At. No. of Ni = 28)

Answer the following:
Co\(^{2+}\) is easily oxidized to Co\(^{3+}\) in the presence of a strong ligand (At. No. of Co = 27).

Write the IUPAC name of the following complex:
[Co(NH₃)₅(CO₃)]Cl.

Write the anode and cathode reactions and the overall cell reaction occurring in a lead storage battery during its use.

Calculate the potential for half-cell containing 0.01 M K\(_2\)Cr\(_2\)O\(_7\)(aq), 0.01 M Cr\(^{3+}\)(aq), and 1.0 x 10\(^{-4}\) M H\(^+\)(aq).

Account for the following:
On the basis of \( E^\circ \) values, O\(_2\) gas should be liberated at anode but it is Cl\(_2\) gas which is liberated in the electrolysis of aqueous NaCl.

Write the cell reaction and calculate the e.m.f. of the following cell at 298 K:
\[ \text{Sn}(s) \mid \text{Sn}^{2+} (\text{0.004 M}) \parallel \text{H}^+ (\text{0.02 M}) \mid \text{H}_2 (\text{1 Bar}) \mid \text{Pt}(s) \]
(Given: \( E^\circ_{\text{Sn}^{2+}/\text{Sn}} = -0.14 \, \text{V}, E^\circ_{\text{H}^+/\text{H}_2} = 0.00 \, \text{V} \))

Account for the following:
Conductivity of CH\(_3\)COOH decreases on dilution.

Which vitamin is responsible for the coagulation of blood?

Which one of the following is a disaccharide?
\[ \text{Glucose, Lactose, Amylose, Fructose} \]