List of top Chemistry Questions asked in CBSE Class XI

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?
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  .
If the speed of light is 3.0×108 ms–1, calculate the distance covered by light in 2.00 ns.
What is the significance of the terms - 'isolated gaseous atom' and 'ground state' while defining the ionization enthalpy and electron gain enthalpy?
Hint: Requirements for comparison purposes.

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

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?
Explain why cations are smaller and anions larger in radii than their parent atoms?
How does atomic radius vary in a period and in a group? How do you explain the variation?
What does atomic radius and ionic radius really mean to you?
Why do elements in the same group have similar physical and chemical properties?