List of top Chemistry Questions asked in CBSE CLASS XII, CBSE Compartment XII

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.
On hydrolysis, which of the following carbohydrates gives only $\mathrm{\beta}$-glucose ?
Why is o-nitrophenol more acidic than o-methoxyphenol?
What happens when acidic solution of potassium permanganate is allowed to stand for sometime ? Give the equation involved. What is this type of reaction called ?
Write mechanism of acid dehydration of ethanol to ethene.
Predict the alkene that would be formed by dehydrohalogenation of 1-Bromo-1-methylcyclohexane.
Give structures of A, B and C: Aniline $\xrightarrow{Br_2/H_2O}$ A $\xrightarrow{NaNO_2+HCl, 0-5^\circ C}$ B $\xrightarrow{H_3PO_2+H_2O}$ C
Explain: (i) Presence of carbonyl group in glucose. (ii) Presence of five $-$OH groups attached to different carbon atoms.
What are reducing sugars?
For decomposition of $H_2O_2$ by $I^-$: Step I: $H_2O_2 + I^- \rightarrow H_2O + IO^-$ (slow). Step II: $H_2O_2 + IO^- \rightarrow H_2O + I^- + O_2$ (fast). (a) Write rate law. (b) Determine order w.r.t. $H_2O_2$ and $I^-$ and overall order. (c) Molecularity of Step II.
Predict the alkene formed by dehydrohalogenation of 1-Bromo-1-methylcyclohexane.
Which isomer of $C_4H_9Br$ is most reactive towards $S_N1$ reaction?
Though chlorine shows strong $-I$ effect, why is it ortho/para directing?
61 g benzoic acid (M = 122 g mol$^{-1}$) dissolved in 500 g benzene. Vapour pressure of pure benzene = 66 torr. Assume complete dimerisation. Calculate vapour pressure of solution.
Under what condition can a bimolecular reaction become kinetically first order?
When $CoCl_3 \cdot 6NH_3$ is mixed with excess $AgNO_3$ solution, 3 moles of $AgCl$ are precipitated per mole. Write its structural formula, IUPAC name, hybridisation and magnetic behaviour (VBT).
Give structures of A, B and C: $CH_3Cl \xrightarrow{KCN}$ A $\xrightarrow{LiAlH_4}$ B $\xrightarrow{CHCl_3 + \text{alc. } KOH, \Delta}$ C
Why is DC not used for measuring resistance of ionic solution?
Draw the structures of major products: (a) Chlorobenzene + $CH_3Cl$ / Na, dry ether
(b) p-Hydroxyphenethyl alcohol + HBr
What happens when: (a) Propanenitrile is treated with phenyl magnesium bromide followed by hydrolysis? (b) p-Fluorotoluene is treated with $CrO_3$ in presence of acetic anhydride followed by hydrolysis with aqueous acid? (c) Phthalic acid is treated with $NH_3$ followed by heating?
Why are products of electrolysis of $AgNO_3$ different with silver electrodes and platinum electrodes?