List of top Questions asked in CBSE CLASS XII

Deficiency of vitamin B$_1$ causes the disease :
Assertion (A): Aquatic species are more comfortable in cold water than in warm water.
Reason (R): Solubility of oxygen gas in water decreases with increase in temperature.
Assertion (A): First ionisation enthalpy of Cr is lower than that of Zn.
Reason (R): Zinc is a non-transition element.

The reaction

suggests that phenol is :

Anilinium hydrogen sulphate on heating at 453–473 K produces which of the following as a major product ?

Which of the following amines does not give foul smell of isocyanide on heating with chloroform and ethanolic KOH ?

Which of the following haloalkanes is most reactive towards S$_N$2 reaction ?
Which of the following is the slope of the first order reaction in the plot of ln[R] vs. time ?
A conductivity cell usually consists of two :
Which of the following aqueous solutions will have the highest osmotic pressure ?
With increase in atomic number, the melting point of transition metals :
An organic compound (X) having molecular formula C$_5$H$_{10$O can show various properties depending on its structures. Draw each of the structures if it :
shows Cannizzaro reaction.
Write the reaction involved in the following :
Clemmensen reduction
Account for the following :
(I) The E$^\circ_{Mn^{2+}/Mn}$ value for manganese is highly negative, whereas E$^\circ_{Mn^{3+}/Mn^{2+}}$ is highly positive.
Calculate the emf of the following cell at 25$^\circ$C :
Zn(s) $\mid$ Zn$^{2+}$ (0.1 M) $\parallel$ H$^+$ (0.01 M) $\mid$ H$_2$(g) (1 bar), Pt(s)
Given: E$^\circ_{Zn^{2+}/Zn}$ = –0.76 V, E$^\circ_{2H^+/H_2}$ = 0.00 V, log 10 = 1
Complete the following ionic equations :
5SO$_3^{2-}$ + 2MnO$_4^-$ + 6H$^+$ ⟶ ?
Answer the following question:
Name two elements of 3d series for which the third ionisation enthalpies are quite high.
How can you convert propanenitrile to 1-aminopropane?
Give reasons for the following:HCHO is more reactive than CH$_3$CHO towards addition of HCN.
Give reasons for the following:
Benzoic acid does not undergo Friedel-Crafts reaction.

Write structure of the products of the following reactions:

Vinyl group directly attached with carboxylic acid should decrease acidity due to resonance, but it increases acidity. Explain.
Essential amino acids and Non-essential amino acids
Peptide linkage and Glycosidic linkage
Write two differences between Amylose and Amylopectin components of starch.