List of top Questions asked in CBSE CLASS XII- 2024

How can you convert phenyl magnesium bromide to benzoic acid?

Arrange the following in increasing order of their reactivity towards HCN: \[ \text{CH}_3\text{COCH}_3, \, (\text{CH}_3)_3\text{C} - \text{COCH}_3, \, \text{CH}_3\text{CHO} \]

Draw structure of the 2,4-dinitrophenylhydrazone of benzaldehyde.

Give a simple chemical test to distinguish between ethanoic acid and ethanal.

Write the products in the following reactions:

Draw the structures of optical isomers of [PtCl\(_2\)(en)\(_2\)]\(^{2+}\).

Out of [Co(NH\(_3\))\(_6\)]\(^{3+}\) and [Co(NH\(_3\))\(_4\)Cl\(_2\)]\(^+\), which complex is heteroleptic and why?

For the coordination compound on the basis of crystal field theory, write the electronic configuration for d\(^4\) ion if \(\Delta_o\) < P. Is the coordination compound a high spin or low spin complex?

What type of isomerism is shown by the complex [Co(NH\(_3\))\(_6\)][Cr(CN)\(_6\)]?

Write the geometry and magnetic behaviour of the complex [Ni(CO)\(_4\)] on the basis of Valency Bond Theory (VBT).

Write the IUPAC name of the following complex: [PtCl\(_2\)(en)\(_2\)](NO\(_3\))\(_2\)

How is the crystal field splitting energy for octahedral complex (\(\Delta_o\)) related to that of tetrahedral complex (\(\Delta_t\))?

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. $[Given : 2 303 R = 19 15 JK^{-1} mol^{-1}, log 3 = 0 48]$

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

Write the reaction involved in the following: Wolff-Kishner reduction
(b) Decarboxylation reaction
(c) Cannizzaro reaction

Write the structures of A, B, and C in the following reactions:

Define the following terms:
(a) Denaturation of protein
(b) Invert sugar

Write the major product in the following reaction:

Why do transition metals have high enthalpy of atomization? Which element of the 3d-series has the lowest enthalpy of atomization?

What is lanthanoid contraction? Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

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?
$[ log 2 = 0·301, log 3 = 0·4771, log 4 = 0·6021 ]$

Transition metals have incomplete d-subshells either in the neutral atom or in their ions. The presence of partly filled d-orbitals in their atoms makes transition elements different from non-transition elements. With partly filled d-orbitals, these elements exhibit certain characteristic properties such as:

• Display of a variety of oxidation states
• Formation of coloured ions
• Entering into complex formation with a variety of ligands

The transition metals and their compounds also exhibit catalytic properties and paramagnetic behaviour. The transition metals are very hard and have low volatility. An examination of the E₀ M₂₊/M values shows the varying trends: