List of top Questions asked in CBSE Class XI

What will be the conjugate bases for the Brönsted acids: HF, H2SO4 and HCO3–?
Define a taxon. Give some examples of taxa at different hierarchical levels.
Given below is the scientific name of Mango. Identify the correctly written name. 
Mangifera Indica
Mangifera indica
What do we learn from identification of individuals and populations?
Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:
\(CH_4 (g) + H_2O (g) ⇋ CO (g) + 3H_2 (g)\)
  1. Write as expression for Kp for the above reaction.
  2. How will the values of Kp and composition of equilibrium mixture be affected by
    1. increasing the pressure
    2. increasing the temperature
    3. using a catalyst?
What different criteria would you choose to classify people that you meet often?
Which of the following reactions will get affected by increasing the pressure? Also, mention whether change will cause the reaction to go into forward or backward direction.
  1. \(COCl_2 (g) ⇋ CO (g) + Cl_2 (g)\)
  2. \(CH_4 (g) + 2S_2 (g) ⇋ CS_2 (g) + 2H_2S (g)\)
  3. \(CO_2 (g) + C (s) ⇋ 2CO (g)\)
  4. \(2H_2 (g) + CO (g) ⇋ CH_3OH (g)\)
  5. \(CaCO_3 (s) ⇋ CaO (s) + CO_2 (g)\)
  6. \(4NH_3 (g) + 5O_2 (g) ⇋ 4NO (g) + 6H_2O(g)\)
Which of the following are Lewis acids? H2O, BF3, H+, and NH4+.
What effect does branching of an alkane chain has on its boiling point?
What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species: HNO2, CN– , HClO4,F–,OH–,CO and S2–
In the alkane \( H_3C-CH_2-C(CH_3)_2-CH_2-CH(CH_3)_2\) , identify 1°,2°,3° carbon atoms and give the number of H atoms bonded to each one of these.
What are the necessary conditions for any system to be aromatic?
Calculate:
  1. ∆GΘ and 
  2. the equilibrium constant for the formation of NO2 from NO and O2 at 298 K
\(NO (g) + \frac 12O_2 (g) ⇋ NO_2 (g)\)
where,
 ∆fGΘ (NO2) = 52.0 kJ/mol
∆fGΘ (NO) = 87.0 kJ/mol
∆fGΘ (O2) = 0 kJ/mol.
How do you account for the formation of ethane during chlorination of methane?
At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO2 in equilibrium with soild carbon has 90.55% CO by mass
\(C(s) + CO_2(g) ⇋ 2CO(g)\)
Calculate Kc for this reaction at the above temperature.
Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches the equilibrium:
\(2BrCl (g) ⇋ Br_2 (g) + Cl_2 (g)\)
for which Kc = 32 at 500 K. If initially pure BrCl is present at a concentration of 3.3 × 10–3 mol L–1, what is its molar concentration in the mixture at equilibrium?
Draw the labelled diagram of the following: 
(i) gram seed 
(ii) V.S. of maize seed
What is meant by the term bond order? Calculate the bond order of: \(N_2\), \(O_2\), \(O_2^+\) and \(O_2^-\) .
Equilibrium constant, Kc for the reaction
\(N_2 (g) + 3H_2 (g) ⇋ 2NH_3 (g)\)
At 500 K is 0.061 At a particular time, the analysis shows that composition of the reaction mixture is 3.0 mol L–1 N2, 2.0 mol L–1 H2 and 0.5 mol L–1 NH3. Is the reaction at equilibrium? If not in which direction does the reaction tend to proceed to reach equilibrium?
One of the reaction that takes place in producing steel from iron ore is the reduction of iron(II) oxide by carbon monoxide to give iron metal and CO2.
\(FeO (s) + CO (g) ⇋ Fe (s) + CO_2 (g);\ K_p = 0.265\  \text {atm}\) at 1050 K
What are the equilibrium partial pressures of CO and CO2 at 1050 K if the initial partial pressures are: \(P_{CO}\) = 1.4 atm and \(P_{CO_2}\) = 0.80 atm?
Describe the various types of placentations found in flowering plants.
(a) How many subshells are associated with n = 4 ? (b) How many electrons will be present in the subshells having ms value of \(-\frac{1}{2}\) for n = 4 ?
Indicate the number of unpaired electrons in : (a) P, (b) Si, (c) Cr, (d) Fe and (e) Kr.
Define hydrogen bond. Is it weaker or stronger than the van der Waals forces?
The unpaired electrons in Al and Si are present in 3p orbital. Which electrons will experience more effective nuclear charge from the nucleus ?