List of top Chemistry Questions asked in CBSE CLASS XII

Assertion (A): The boiling points of alkyl halides decrease in the order: RI > RBr > RCl > RF.
Reason (R): The boiling points of alkyl chlorides, bromides and iodides are considerably higher than that of the hydrocarbon of comparable molecular mass.

Assertion (A): [Cr(H$_2$O)$_6$]Cl$_2$ and [Fe(H$_2$O)$_6$]Cl$_2$ are examples of homoleptic complexes.
Reason (R): All the ligands attached to the metal are the same.

An unripe mango placed in a concentrated salt solution to prepare pickle, shrivels because __________

The best reagent for converting propanamide into propanamine is:

The acid formed when propyl magnesium bromide is treated with CO$_2$ followed by acid hydrolysis is:

Alkyl halides undergoing nucleophilic bimolecular substitution reaction involve:

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

Acidified KMnO$_4$ oxidizes sulphite to:

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:

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:

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:

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

The role of a catalyst is to change _____________ .

Why is [Ni(CN)4]2- square planar while [Ni(CO)4] is tetrahedral? [Atomic number : Ni = 28]

Identify A and B in the following reactions:

Shweta mixed two liquids A and B of 10 mL each. After mixing, the volume of the solution was found to be 20.2 mL.
(i) Why was there a volume change after mixing the liquids?
(ii) Will there be an increase or decrease of temperature after mixing?
(iii) Give one example for this type of solution.

Give a chemical test to distinguish between benzaldehyde and acetophenone.

Which of the following molecules is chiral in nature?

While doing qualitative analysis in chemistry lab, Abhishek added yellow coloured potassium chromate solution into a test tube. He was surprised to see the colour of the solution changing immediately to orange. He realised that the test tube was not clean and contained a few drops of some liquid. Which of the following substances will be the most likely liquid to be present in the test tube before adding potassium chromate solution?

Tertiary alkyl halides are least reactive towards SN2 reaction.

Based on the data given above, give plausible reason for the variation of conductivity and molar conductivity with concentration.

Concentration of KCl solution (mol/L)	Conductivity at 298.15 K (S cm-1)	Molar Conductivity at 298.15 K (S cm2 mol-1)
1.000	0.1113	111.3
0.100	0.0129	129.0
0.010	0.00141	141.0

Among the following, which will have inversion of configuration on reaction with aqueous alkali and why?
(i) 1-chloropropane
(ii) 2-chloro-2-methylpropane

Calculate the molality of a solution prepared by dissolving 5 g of NaOH in 450 g of water. (Molar mass of NaOH = 40 g/mol)

Calculate the packing efficiency in a face-centered cubic (FCC) crystal.