List of top Chemistry Questions asked in CBSE CLASS XII

How do you explain the following ? (a) Presence of a carbonyl group in glucose (b) Presence of five --OH groups in glucose

For a reaction A + B $\rightarrow$ Products, the rate law is : \[ \text{Rate} = k[A]^{\frac{3}{2}}[B] \] Write the overall order of the reaction. Can this reaction be an elementary reaction ? Give reason in support of your answer.

Give reasons for the following : (a) Alkyl halides, though polar, yet their solubility in water is very low.

Give reasons for the following : (b) p-Dichlorobenzene has higher melting point than those of o- and m-isomers.

For the compound having molecular formula C$_4$H$_9$Br, write : (a) the isomer which is most reactive towards SN1 displacement. (b) the isomer which, on reacting with Na metal in the presence of dry ether, gives 2,5-Dimethylhexane.

Assertion (A) : Aromatic primary amines can easily be prepared by Gabriel phthalimide synthesis. Reason (R) : Gabriel phthalimide synthesis is used to prepare only aliphatic primary amines.

Assertion (A) : Phenol is more acidic than 4-methylphenol. Reason (R) : The presence of an electron releasing group in phenol makes it more acidic.

Define the following terms with a suitable example in each case : \[ (i)\ \text{Ambidentate ligand} \] \[ (ii)\ \text{Double salt} \]

Explain why, on addition of 1 mol of KCl to 1 litre of water, the boiling point of water increases, while the addition of 1 mol of methyl alcohol to 1 litre of water decreases the boiling point.

Assertion (A) : Order of reaction is not applicable for elementary reaction but applicable for complex reaction. Reason (R) : Order of reaction is an experimental quantity.

Write IUPAC names of the following compounds : \[ (i)\ [PtCl_2(en)_2]SO_4 \] \[ (ii)\ (NH_4)_2[CoF_4] \]

For the reaction \(2A \rightarrow 3B\), the rate of reaction \(\frac{d[B]}{dt}\) is equal to :

On hydrolysis, which of the following carbohydrates gives only glucose ?

Assertion (A) : Separation of Zr and Hf is difficult. Reason (R) : Zr and Hf have almost identical atomic and ionic radii due to lanthanoid contraction.

In aqueous acidified solution, CrO$_4^{2-}$ ion converts to which of the following ?

The boiling point of an azeotropic mixture of water and nitric acid is more than that of pure water and nitric acid. The mixture shows :

According to Werner’s theory, the primary valencies of the central metal atom :

Among the following, which one has the lowest value of pK$_b$ ?

Which reagent is used to distinguish between C$_2$H$_5$NH$_2$ and (C$_2$H$_5$)$_2$NH ?

The dehydration of 1$^\circ$, 2$^\circ$ and 3$^\circ$ alcohols follows the order :

The oxidation number of Co in [Co(NH$_3$)$_5$(ONO)]SO$_4$ is :

Which of the following compounds is most reactive towards nucleophilic substitution reaction with aqueous NaOH ?

The mole fraction of a solute in 2.0 molal aqueous solution is :

On electrolysis of very dilute aqueous solution of NaCl using platinum electrodes :

Answer the following: \[ (a)(i)\;\text{Calculate the electrode potential of a half-cell for zinc electrode dipping in }0.01M\;ZnSO_4\text{ solution at }25^\circ C. \] \[ E^\circ_{Zn^{2+}/Zn}=-0.76V,\quad \log 10=1 \] \[ (a)(ii)\;\text{Write anode, cathode and overall reaction involved in dry cell.} \] \[ (a)(iii)\;\text{Equilibrium constant }(K_c)\text{ is related to }E^\circ_{\text{cell}},\text{ but not to }E_{\text{cell}}.\text{ Why?} \]