List of top Questions asked in CBSE Class XI

The acceleration due to gravity on the surface of moon is 1.7 ms-2.What is the time period of a simple pendulum on the surface of moon if its time period on the surface of earth is 3.5 s? (g on the surface of earth is 9.8 ms-2

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that? 
What is the basic difference in approach between the Mendeleev's Periodic Law and the Modern Periodic Law?
On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.
In terms of period and group where would you locate the element with Z =114?
Write the atomic number of the element present in the third period and seventeenth group of the periodic table.
Which element do you think would have been named by
(i) Lawrence Berkeley Laboratory
(ii) Seaborg's group?
Why do elements in the same group have similar physical and chemical properties?
What does atomic radius and ionic radius really mean to you?
How does atomic radius vary in a period and in a group? How do you explain the variation?
Explain why cations are smaller and anions larger in radii than their parent atoms?
Anything that influences the valence electrons will affect the chemistry of the element. Which one of the following factors does not affect the valence shell?

The size of isoelectronic species - F-, Ne and Na+ is affected by

What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?
The first ionization enthalpy values (in kJmol-1 ) of group 13 elements are :
BAlGaInTl
801577579558589
How would you explain this deviation from the general trend?
Which of the following pairs of elements would have a more negative electron gain enthalpy? 
  1. O or F 
  2. F or Cl
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?
How are 0.50 mol Na2CO3 and 0.50 M Na2CO3 different?
If 10 volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?
Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
(i) Calculate the number of electrons which will together weigh one gram.
(ii) Calculate the mass and charge of one mole of electrons.
Convert the following into basic units:
  1. 28.7 pm
  2. 15.15 pm
  3. 25365 mg
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?
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?
Energy of an electron in the ground state of the hydrogen atom is -2.18 x 10-18  J. Calculate the ionization enthalpy of atomic hydrogen in terms of J mol-1  .