List of top Questions asked in CBSE Class XI

The longest wavelength doublet absorption transition is observed at 589 and 589.6 nm. Calculate the frequency of each transition and energy difference between two excited states.
Write Lewis dot symbols for atoms of the following elements: Mg, Na, B, O, N, Br.
In astronomical observations, signals observed from the distant stars are generally weak. If the photon detector receives a total of 3.15 × 10–18 J from the radiations of 600 nm, calculate the number of photons received by the detector.
Give the schematic representation of glycolysis?
Explain why pure liquids and solids can be ignored while writing the equilibrium constant expression?
Give the schematic representation of an overall view of Krebs’ cycle.
For the following equilibrium, \(K_c = 6.3 × 10^{14}\) at \(1000\  K\)
\(NO (g) + O_3 (g) ⇋ NO_2 (g) + O_2 (g)\)
Both the forward and reverse reactions in the equilibrium are elementary bimolecular reactions. What is \(K'_c\) for the reverse reaction?
Explain ETS.
The skeletal structure of CH3COOH as shown below is correct, but some of the bonds are shown incorrectly. Write the correct Lewis structure for acetic acid.
The skeletal structure of CH3COOH
Explain the process of inspiration under normal conditions.
Arrange the bonds in order of increasing ionic character in the molecules: LiF, K2O, N2, SO2 and ClF3.
Define electronegativity. How does it differ from electron gain enthalpy?
Write the expression for the equilibrium constant, Kc for each of the following reactions: 
  1. \(2NOCl (g) ⇋ 2NO (g) + Cl_2 (g)\)
  2. \(2Cu(NO_3)_2 (s) ⇋ 2CuO (s) + 4NO_2 (g) + O_2 (g)\)
  3. \(CH_3COOC_2H_5(aq) + H_2O(l) ⇋ CH_3COOH (aq) + C_2H_5OH (aq)\)
  4. \(Fe^{3+} (aq) + 3OH^– (aq) ⇋ Fe(OH)_3 (s)\)
  5. \(I_2 (s) + 5F_2 ⇋ 2IF_5\)
Write the significance/applications of dipole moment.
Find out the value of \(K_c\) for each of the following equilibria from the value of \(K_p\): 
  1. \(2NOCl (g) ⇋ 2NO (g) + Cl_2 (g); \ K_p= 1.8 × 10^{–2}\  at \ 500\ K\)
  2. \(CaCO_3 (s) ⇋ CaO(s) + CO_2(g); \ K_p= 167 \ at \ 1073\  K\)
Use Lewis symbols to show electron transfer between the following atoms to form cations and anions:
  1. K and S 
  2. Ca and O 
  3. Al and N.
What is the difference between lymph and blood?
Write the resonance structures for SO3 , NO2 and NO3-
Explain the important aspects of resonance with reference to the \(CO_3^{2-}\) ion.
Although geometries of NH3 and H2O molecules are distorted tetrahedral, bond angle in water is less than that of ammonia. Discuss.
Discuss the shape of the following molecules using the VSEPR model: 
BeCl2, BCl3, SiCl4, AsF5, H2S, PH3
Define octet rule. Write its significance and limitations.
How does cytokinesis in plant cells differ from that in animal cells?
Considering the elements F, Cl, O and N, the correct order of their chemical reactivity in terms of oxidizing property is:
Describe the evolutionary change in the pattern of heart among the vertebrates.