List of top Questions asked in CBSE CLASS XII

Compounds of transition metals are generally coloured. Give reason.
Why are transition elements good catalysts?
Why is first ionization enthalpy of chromium lower than that of Zn?
What is Lanthanoid contraction?
Why Zinc is not regarded as a transition element?
Predict whether \([CoF_6]^{3-}\) is diamagnetic or paramagnetic and why?
\([Atomic \ \ number : Co = 27]\)
Show that the time required for 99.9% completion in a first-order reaction is 10 times of half-life (t$_{1/2}$) of the reaction.
What happens when ethyl chloride is treated with alcoholic potassium hydroxide?
The presence of –NO$_2$ group at ortho or para position increases the reactivity of haloarenes towards nucleophilic substitution reactions. Give reason to explain the above statement.
Write the IUPAC name of the given compound:
3– Bromo– 1 chlorocyclohexene
Explain the following terms:
(a) Essential amino acids:
(b) Peptide bond:
(c) Denaturation:
Which one of the given compounds is a stronger acid and why?
CH$_2$FCH$_2$COOH or CH$_3$CHFCH$_2$COOH
Give chemical tests to distinguish between the following pairs of compounds:
(i) Phenol and Benzoic acid:
(ii) Propanal and Propanone:
Calculate emf of the following cell at 25°C:
Sn/Sn$^{2+}$(0.001 M) || H$^+$(0.01 M) | H$_2$(g)(1 bar) | Pt(s)
Given: E°(Sn$^{2+}$/Sn) = -0.14 V, E° H$^+$/H$_2$ = 0.00 V (log 10 = 1)
What is meant by a unidentate ligand? Give an example.
Write the electronic configuration for d$^4$ ion if \( \Delta_0 < P \) on the basis of crystal field theory.
Draw the geometrical isomers of the given complex:
[Pt(en)2Cl2]2+
Two bases are mentioned below, identify which is present in DNA and which one is present in RNA: 
(i) Thymine 
(ii) Uracil.
 
What happens when glucose reacts with bromine water? Write the chemical equation.
Arrange the following compounds in the increasing order of their boiling points:
Butane, 1-Bromobutane, 1-Iodobutane, 1-Chlorobutane
Which compound in the given pair will undergo S$_N$2 reaction at a faster rate and why?
CH$_3$–CH$_2$–I and CH$_3$–CH$_2$–Br
18 g of a non-volatile solute is dissolved in 200 g of H$_2$O, and it freezes at 272.07 K. Calculate the molecular mass of the solute (K$_f$ for water = 1.86 K kg mol$^{-1}$).
Define the following terms:
(a) Order of Reaction:
(b) Activation Energy:
Assertion (A): Benzoic acid does not undergo Friedel – Crafts reaction.
Reason (R): Carboxyl group is deactivating and the catalyst aluminium chloride gets bonded to the carboxyl group.
The general electronic configuration of d-block elements is: