List of top Questions asked in CBSE CLASS XII

Arrange the following in the increasing order of their basicity in an aqueous solution:
$\text{(CH}_3\text{)}_3\text{N}, \ \text{(CH}_3\text{)}_2\text{NH}, \ \text{NH}_3, \ \text{CH}_3\text{NH}_2$

Complete and balance the following chemical equations:
(a) \(\text{MnO}_4^- + \text{C}_2\text{O}_4^{2-} + \text{H}^+ \to \) (b) \(\text{KMnO}_4 \xrightarrow{\text{Heat}} \) (c) \(\text{Cr}_2\text{O}_7^{2-} + \text{H}_2\text{S} + \text{H}^+ \to \)

Using valence bond theory, explain the hybridization and magnetic character of the following: (a) [Co(NH$_3$)$_6$]$^{3+}$ (b) [Ni(CO)$_4$]

Define the following: (i) Enantiomers
(ii) Racemic mixture

Why is chlorobenzene resistant to nucleophilic substitution reaction?

Examine the following observations: (a) Transition elements generally form coloured compounds.
(b) Zinc is not regarded as a transition element.

Name the following coordination compounds according to IUPAC norms: (a) [Co(NH$_3$)$_4$(H$_2$O)Cl]Cl$_2$
(b) [CrCl$_2$ (en)$_2$]Cl

Arrange the following compounds in increasing order of their reactivity towards SN2 displacement:
\[ \text{2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane} \]

At 25°C the saturated vapour pressure of water is 24 mm Hg. Find the saturated vapour pressure of a 5% aqueous solution of urea at the same temperature. (Molar mass of urea = 60 g mol$^{-1}$)

Assertion (A): Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis.
Reason (R): Ary1 halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide.

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.

Define the following terms:
(a) Pseudo first-order reaction
(b) Half-life period of reaction (\(t_{1/2}\))

Assertion (A): In a first order reaction, if the concentration of the reactant is doubled, its half-life is also doubled.
Reason (R): The half-life of a reaction does not depend upon the initial concentration of the reactant in a first order reaction.