List of top Questions asked in CBSE Class XI

What is the difference between distillation, distillation under reduced pressure and steam distillation?
Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.
Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles. 
(a) \(CH_3COOH+HO^{–6} \rightarrow CH_3COO^–+H_2O\) 
(b) \(CH_3COCH^{3+} C^–N\rightarrow (CH_3)_2C(CN)(OH)\)
(c) \(C_6H_6 + CH_3C+O^+ \rightarrow C_6H_5COCH_3\)
Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL–1 and the mass per cent of nitric acid in it being 69%.
What are electrophiles and nucleophiles? Explain with examples.
Which of the two, \(O+2NCH_2CH_2O^- \,or \,CH_3CH_2O^–\)is expected to be more stable and why?
Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:
  1. \(2AgBr (s) + C_6H_6O_2(aq) \rightarrow 2Ag(s) + 2HBr (aq) + C_6H_4O_2(aq)\)
  2. \(HCHO(l) + 2[Ag (NH_3)_2] ^+ (aq) + 3OH^ - (aq) \rightarrow 2Ag(s) + HCOO ^- (aq) + 4NH_3(aq) + 2H_2O(l)\)
  3. \(HCHO (l) + 2Cu^{ 2+}(aq) + 5 OH^ - (aq) \rightarrow Cu_2O(s) + HCOO ^- (aq) + 3H_2O(l)\)
  4. \(N_2H_4(l) + 2H_2O_2(l) \rightarrow N_2(g) + 4H_2O(l)\)
  5. \(Pb(s) + PbO_2(s) + 2H_2SO_4(aq) \rightarrow  2PbSO_4(s) + 2H_2O(l)\)
Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wavenumber (v) of the yellow light
Give the IUPAC names of the following compounds:
IUPAC names of compounds
(f) Cl2CHCH2OH
An ion with mass number 37 possesses one unit of negative charge. If the ion conatins 11.1% more neutrons than the electrons, find the symbol of the ion.
Calculate the oxidation number of Sulphur, chromium, and nitrogen in
\(H_2SO_5\), \(Cr_2O_7^{2−}\) and \(NO_3^−\). Suggest structure of these compounds. Count for the fallacy.
Write bond line formulas for, Isopropyl alcohol, 2,3-Dimethylbutanal, Heptan-4-one.
Indicate the σ and π bonds in the following molecules. \(C_6H_6, C_6H_{12}, CH_2Cl_2, CH_2=C=CH_2, CH3NO2, HCONHCH_3.\)
A certain particle carries 2.5 × 10–16 C of static electric charge. Calculate the number of electrons present in it.
How many electrons in an atom may have the following quantum numbers?
  1. n = 4, ms = – \(\frac 12\)
  2. n = 3, l = 0
Consider the reactions: 
(a) \(6 \,CO_2(g) + 6H_2O(l) \rightarrow C_6H_{12}O_6(aq) + 6O_2(g)\) 
(b) \(O_3(g) + H_2O_2(l) \rightarrow  H_2O(l) + 2O_2(g)\) 
Why it is more appropriate to write these reactions as: (a) \(6\,CO_2(g) + 12H_2O(l) \rightarrow  C_6H_{12}O_6(aq) + 6H_2O(l) + 6O_2(g)\) 
(b) \(O_3(g) + H_2O_2(l) \rightarrow H_2O(l) + O_2(g) + O_2(g)\) 
Also suggest a technique to investigate the path of the above (a) and (b) redox reactions.
  1. An atomic orbital has n = 3. What are the possible values of l and ml?
  2. List the quantum numbers (ml and l) of electrons for 3d orbital.
  3. Which of the following orbitals are possible?
    1p, 2s, 2p and 3f
Which of the following are isoelectronic species i.e., those having the same number of electrons?
\(Na^+, K^+, Mg^{2+}, Ca^{2+}, S^{2–}, Ar\)
Whenever a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess, and a compound of higher oxidation state is formed if the oxidising agent is in excess. Justify this statement giving three illustrations..
The mass of an electron is 9.1 × 10–31 kg. If its K.E. is 3.0 × 10–25 J, calculate its wavelength.
Calculate the wavelength of an electron moving with a velocity of \(2.05×10^7 \ ms^{–1}\).
Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.
The electron energy in hydrogen atom is given by \(E_n = \frac {(–2.18×10^{–18})}{n^2} \ J\). Calculate the energy required to remove an electron completely from the n = 2 orbit. What is the longest wavelength of light in cm that can be used to cause this transition?
The Mn3+ ion is unstable in solution and undergoes disproportionation to give Mn2+ , MnO2, and H+ ion. Write a balanced ionic equation for the reaction.
What is the energy in joules, required to shift the electron of the hydrogen atom from the first Bohr orbit to the fifth Bohr orbit and what is the wavelength of the light emitted when the electron returns to the ground state ? The ground state electron energy is –2.18×10–11 ergs.