List of top Questions asked in CBSE CLASS XII

Write the IUPAC name of the following complex: [PtCl\(_2\)(en)\(_2\)](NO\(_3\))\(_2\)
Draw the structures of optical isomers of [PtCl\(_2\)(en)\(_2\)]\(^{2+}\).
Write the geometry and magnetic behaviour of the complex [Ni(CO)\(_4\)] on the basis of Valency Bond Theory (VBT).
What type of isomerism is shown by the complex [Co(NH\(_3\))\(_6\)][Cr(CN)\(_6\)]?
Write the products in the following reactions:
reaction of acetophenone
Account for the following:
1. Oxidation of aldehydes is easier as compared to ketones.
2. The alpha (α) hydrogen atoms of aldehydes are acidic in nature.
Out of [Co(NH\(_3\))\(_6\)]\(^{3+}\) and [Co(NH\(_3\))\(_4\)Cl\(_2\)]\(^+\), which complex is heteroleptic and why?
How is the crystal field splitting energy for octahedral complex (\(\Delta_o\)) related to that of tetrahedral complex (\(\Delta_t\))?
Calculate emf of the following cell: \[ \text{Zn (s)} | \text{Zn}^{2+} (0.1 M) || \text{Sn}^{2+} (0.001 M) | \text{Sn (s)} \] Given: \[ E^\circ_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V}, \quad E^\circ_{\text{Sn}^{2+}/\text{Sn}} = -0.14 \, \text{V} \] \[ [\log 10 = 1] \]
Give reasons for the following: (a) Chlorine is ortho/para directing in electrophilic aromatic substitution reactions, though chlorine is an electron withdrawing group.
(b) Racemic mixture is optically inactive.
(c) Allyl chloride is hydrolysed more readily than n-propyl chloride.
Give the equations of reactions for the preparation of: (any three) (a) Phenol from chlorobenzene
(b) Salicyaldehyde from phenol
(c) 2-Methoxyacetophenone from anisole
The rate of a gaseous reaction triples when temperature is increased from 17°C to 27°C. Calculate the energy of activation for this reaction. $[Given : 2 303 R = 19 15 JK^{-1} mol^{-1}, log 3 = 0 48]$
Write the major product in the following reaction:
ethyl chloride (CH3CH2Cl)
Why do transition metals have high enthalpy of atomization? Which element of the 3d-series has the lowest enthalpy of atomization?
Define the following terms:
(a) Denaturation of protein
(b) Invert sugar
Write the structures of A, B, and C in the following reactions:
structures of A, B, and C
In the following pair of compounds, which compound undergoes an $\text{S}_{N}$2 reaction faster and why?
compound undergoes an SN2
Write the reaction involved in the following: Wolff-Kishner reduction
(b) Decarboxylation reaction
(c) Cannizzaro reaction
What is lanthanoid contraction? Actinoid contraction is greater from element to element than lanthanoid contraction. Why?
Assertion (A): Diazonium salts of aromatic amines are more stable than those of aliphatic amines. Reason (R): Diazonium salts of aliphatic amines show resonance.
Assertion (A): p-Nitroaniline is a weaker base than p-toluidine. Reason (R): The electron-withdrawing effect of \(-NO_2\) group in p-nitroaniline makes it a weaker base.
Assertion (A): Uracil base is present in DNA. Reason (R): DNA undergoes self-replication.
A first-order reaction has a rate constant \( 1.25 \times 10^{-3} \, s^{-1} \). How long will 5 g of this reactant take to reduce to 2.5 g?
$[ log 2 = 0·301, log 3 = 0·4771, log 4 = 0·6021 ]$
For the elementary reaction \( P \to Q \), the rate of disappearance of ‘P’ increases by a factor of 8 upon doubling the concentration of ‘P’. The order of the reaction with respect to ‘P’ is:
An azeotropic solution of two liquids has a boiling point lower than either of them when it: