List of top Chemistry Questions asked in CBSE CLASS XII

18 g of a non-volatile solute is dissolved in 200 g of H$_2$O, and it freezes at 272.07 K. Calculate the molecular mass of the solute (K$_f$ for water = 1.86 K kg mol$^{-1}$).

Arrange the following compounds in the increasing order of their boiling points:
Butane, 1-Bromobutane, 1-Iodobutane, 1-Chlorobutane

What happens when glucose reacts with bromine water? Write the chemical equation.

Which compound in the given pair will undergo S$_N$2 reaction at a faster rate and why?
CH$_3$–CH$_2$–I and CH$_3$–CH$_2$–Br

Define the following terms:
(a) Order of Reaction:
(b) Activation Energy:

Assertion (A): Benzoic acid does not undergo Friedel – Crafts reaction.
Reason (R): Carboxyl group is deactivating and the catalyst aluminium chloride gets bonded to the carboxyl group.

Assertion (A): p-nitrophenol is less acidic than phenol.
Reason (R): Nitro group is electron-withdrawing and helps in the stabilization of p-nitrophenoxide ion.

Assertion (A): Fructose is a reducing sugar.
Reason (R): Fructose does not reduce Fehling solution and Tollen’s reagent.

Assertion (A): For a Daniell cell, Zn/Zn$^{2+}$(1M) || Cu$^{2+}$(1M)/Cu with \( E_{\text{cell}} = 1.1 \, V \), if the external opposing potential is more than 1.1 V, the electrons flow from Cu to Zn.
Reason (R): Cell acts like a galvanic cell.

Match the reagents required for the given reactions: I. Oxidation of primary alcohols to aldehydes (p) \(NaBH_4\)
II. Butan-2-one to Butan-2-ol (q) 85% phosphoric acid at 440 K
III. Bromination of Phenol to 2, 4, 6- (r) PCC Tribromophenol
IV. Dehydration of propan-2-ol to (s) Bromine water propene

The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometrical shapes of coordination compounds whereas ’The Crystal Field Theory’ for coordination compounds is based on the effect of different crystal fields (provided by ligands taken as point charges), on the degeneracy of d-orbital energies of the central metal atom/ion. The splitting of the d-orbitals provides different electronic arrangements in strong and weak crystal fields. The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. Coordination compounds find extensive applications in metallurgical processes, analytical and medicinal chemistry.
Answer the following questions:

Write the structures of A and B in the following reaction: \[ \text{C}_6\text{H}_5\text{COOH} \xrightarrow{\text{NH}_3, \Delta} A \xrightarrow{\text{Br}_2/\text{NaOH}} B \]

Complete the following reaction: \[ \text{C}_6\text{H}_5\text{N}_2^+Cl^- \xrightarrow{\text{(i) HBF}_4} \xrightarrow{\text{(ii) NaNO}_2/\text{Cu}, \Delta} \quad ? \]

How will you convert aniline to p-bromoaniline?

Write a simple chemical test to distinguish between methylamine and aniline.

Write the chemical reaction involved in Gabriel phthalimide synthesis.

Why are equimolar solutions of sodium chloride and glucose not isotonic?

Out of chlorobenzene and 2,4,6-trinitrochlorobenzene, which is more reactive towards nucleophilic substitution and why?

Draw the structures of major monohalo products in each of the following reactions:

Assertion (A): When NaCl is added to water, elevation in boiling point is observed. Reason (R): Elevation in boiling point is a colligative property.

Assertion (A): Transition metals have high enthalpy of atomization. Reason (R): This is because transition metals have low melting points.

Assertion (A): The pK$_a$ of O$_2$N–CH$_2$–COOH is lower than that of CH$_3$–COOH. Reason (R): The –NO$_2$ group shows an electron-withdrawing effect, which increases the acidic character of O$_2$N–CH$_2$–COOH.