List of top Chemistry Questions asked in CBSE CLASS XII

Assertion (A) : It is not possible to separate the components of an azeotrope by fractional distillation.

Reason (R) : Minimum boiling azeotrope is formed by the solutions showing large positive deviation from Raoult's law.

The secondary valency of Co in \( \mathrm{[Co(en)_3]^{3+}} \) is

At low temperature, phenol on reaction with \( \mathrm{Br_2} \) in \( \mathrm{CS_2} \) gives

\( \mathrm{CH_3-NH_2} \) on reaction with \( \mathrm{(CH_3CO)_2O} \) gives

Identify "X" in the following reaction :

\( \mathrm{CH_3-CO-CH_2-CO-O-CH_3} \xrightarrow{\mathrm{NaBH_4}} \text{X} \)

"X" is

How the conductivity varies on decreasing concentration for both weak and strong electrolytes ?

The activation energy of a reaction can be determined from the slope of which of the following curves ?

In the ring structure of fructose, the anomeric carbon is

Which of the following transition metals has lowest enthalpy of atomisation ?

Which of the following is the correct expression of \( K_f \) which depends upon the nature of solvent ?

Define the following terms:

(a) Anomers

(b) Invert sugar

(c) Glycosidic linkage

(b) Answer the following questions:

(i) Name a member of the lanthanoid series

(I) which exhibits +4 oxidation state

(II) which exhibits +2 oxidation state.

(ii) Why transition metals act as good catalyst?

(iii) Why Cr has higher melting point than Mn?

(b) Answer the following questions :

(i) Draw structure of the 2, 4-dinitrophenyl hyzdrazone derivative of benzaldehyde.

(ii) Arrange the following in increasing order of their reactivity towards HCN :

Di-tert. butyl ketone, Acetaldehyde, Acetone

(iii) Give a simple chemical test to distinguish between benzoic acid and ethyl benzoate.

(iv) Write the name of the reagent to convert Ethanenitrile to Ethanal.

(v) Draw the structure of 'X' in the following reaction :



(i) From the given data of \( E^\circ \) values, answer the following questions:

MVCrMnFeCoNiCu
\( E^\circ_{\mathrm{M^{2+}/M}} \)-1.18-0.91-1.18-0.44-0.28-0.25+0.34

(I) Why \( E^\circ_{\mathrm{M^{2+}/M}} \) show irregular trend in the above values?

(II) Why is \( E^\circ_{\mathrm{Cu^{2+}/Cu}} \) value exceptionally positive?

(III) Why \( E^\circ_{\mathrm{Mn^{2+}/Mn}} \) value is highly negative?

(ii) Write the ionic equations for the oxidising action of potassium permanganate for its reaction with \( \mathrm{I^-} \) in both acidic and alkaline solutions.

The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometry of coordination compounds. The Crystal Field Theory (CFT) of coordination compounds is based on the effect of different crystal fields (provided by the 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.

Answer the following question :

(b) Using crystal field theory, write the electronic configuration of central metal atom/ion of the following :

(i) \( \mathrm{[CoF_6]^{3-}} \)

(ii) \( \mathrm{[Co(NH_3)_6]^{3+}} \)

[At. No. : Co = 27]

The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometry of coordination compounds. The Crystal Field Theory (CFT) of coordination compounds is based on the effect of different crystal fields (provided by the 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.

Answer the following question :

(c) Write hybridization and magnetic behaviour of the complex \( \mathrm{[Fe(CN)_6]^{3-}} \).

[Atomic No. : Fe = 26]

The reaction of amines with mineral acids to form ammonium salts shows that these are basic in nature. Aliphatic amines are stronger bases than ammonia whereas aromatic amines are weaker bases than ammonia. Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides and esters by nucleophilic substitution reaction. The main problem encountered during electrophilic substitution reactions of aromatic amines is that of their high reactivity. Substitution tends to occur at ortho-and para-positions. Hinsberg reagent is used for the identification and distinction between primary, secondary and tertiary amines. Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes.

Answer the following question :

(b) How can you convert aniline to benzonitrile ?

Differentiate between the following :

(i) Peptide linkage and Glycosidic linkage

(ii) Essential amino acids and Non-essential amino acids

Assertion (A) : The pentaacetate of glucose does not react with \( \mathrm{H_2N-OH} \).

Reason (R) : It indicates the presence of free \( \mathrm{-CHO} \) group in glucose.

The deficiency of which of the following vitamins causes increased fragility of red blood cells and muscular weakness :

Why do transition metals show variable oxidation states?
Out of Mn\(^{2+}\) and Zn\(^{2+}\), which ion will be more paramagnetic and why? (Atomic numbers: Mn = 25, Zn = 30)
Why are magnesium blocks attached to iron water pipelines?
Vitamin $B_{12}$ is a complex compound of :
Write any two fat soluble vitamins.