List of top Questions asked in CBSE Class XI

How do you express the bond strength in terms of bond order?
Write the favourable factors for the formation of ionic bond.
How many significant figures should be present in the answer of the following calculations?
  1. \(\frac {0.02856 × 298.15 × 0.112}{0.5785}\)
  2. \(5 × 5.364\)
  3. \(0.0125 + 0.7864 + 0.0215\)
What will be the mass of one \(^{12}C\) atom in g?
Match the following (column I with column II) Column I Column II (a) Chlamydomonas (i) Moss (b) Cycas (ii) Pteridophyte (c) Selaginella (iii) Algae (d) Sphagnum (iv) Gymnosperm

Draw the Lewis structures for the following molecules and ions: \(H_2S\), \(SiCl_4\), \(BeF_2\), \(CO_3^{2-}\) , \(HCOOH\)

Calculate the molarity of a solution of ethanol in water, in which the mole fraction of ethanol is 0.040 (assume the density of water to be one).

Write the complete symbol for the atom with the given atomic number (Z) and atomic mass (A) 
(i) Z = 17, A = 35
(ii) Z = 92, A = 233
(iii) Z = 4, A = 9

How many neutrons and protons are there in the following nuclei? \(_{6}^{13}\textrm{C}\), \(_{8}^{16}\textrm{O}\), \(_{12}^{24}\textrm{Mg}\), \(_{26}^{56}\textrm{Fe}\), \(_{38}^{88}\textrm{Sr}\).

Which one of the following will have the largest number of atoms?
Explain the formation of a chemical bond.

(i) Calculate the total number of electrons present in one mole of methane.
(ii) Find (a) the total number and (b) the total mass of neutrons in 7 mg of 14C. (Assume that the mass of a neutron = 1.675 × 10–27 kg).
(iii) Find (a) the total number and (b) the total mass of protons in 34 mg of NH3 at STP. Will the answer change if the temperature and pressure are changed?

Describe the theory associated with the radius of an atom as it 
  1. gains an electron 
  2. loses an electro
How would you react to the statement that the electronegativity of N on Pauling scale is 3.0 in all the nitrogen compounds?
What is the basic difference between the terms electron gain enthalpy and electronegativity?
Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.
(i) Calculate the number of electrons which will together weigh one gram.
(ii) Calculate the mass and charge of one mole of electrons.
If 10 volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?
How are 0.50 mol Na2CO3 and 0.50 M Na2CO3 different?
Dinitrogen and dihydrogen react with each other to produce ammonia according to the following chemical equation: \(N_2 (g) + H_2 (g) → 2NH_3 (g)\)
  1. Calculate the mass of ammonia produced if 2.00 × 103 g dinitrogen reacts with 1.00 × 103 g of dihydrogen.
  2. Will any of the two reactants remain unreacted?
  3. If yes, which one and what would be its mass?
Which of the following pairs of elements would have a more negative electron gain enthalpy? 
  1. O or F 
  2. F or Cl
What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?
How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?
In a reaction \(A + B_2 → AB_2\) Identify the limiting reagent, if any, in the following reaction mixtures.
  1. 300 atoms of A + 200 molecules of B
  2. 2 mol A + 3 mol B
  3. 100 atoms of A + 100 molecules of B
  4. 5 mol A + 2.5 mol B
  5. 2.5 mol A + 5 mol B
Among the second period elements the actual ionization enthalpies are in the order 
Li < B < Be < C < O < N < F < Ne. 
Explain why 
  1. Be has higher ΔiH than B
  2. O has lower ΔiH than N and F?