List of top Questions asked in CBSE Class XI

The increasing order of reactivity among group 1 elements is \(Li\) \(<Na\) \(<K\) \(<Rb\) \(<Cs\) 
whereas that among group 17 elements is \(F>Cl>Br>I\) Explain.

Assign the position of the element having outer electronic configuration

1. \(ns^ 2 np^ 4\) for \(n\) = \(3\) 
2. \((n - 1)d^ 2 \;ns^ 2\) for \(n\) =\( 4\), and 
3. \((n - 2) f ^7 (n - 1)d ^1 ns^ 2\) for \(n\) = \(6\), in the periodic table.

Predict the formula of the stable binary compounds that would be formed by the combination of the following pairs of elements.

1. Lithium and oxygen 
2. Magnesium and nitrogen 
3. Aluminium and iodine 
4. Silicon and oxygen
5. Phosphorus and fluorine 
6. Element 71 and fluorine

A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.

1. What is the initial effect of the change on vapour pressure?
2. How do rates of evaporation and condensation change initially?
3. What happens when equilibrium is restored finally and what will be the final vapour pressure?

In the modern periodic table, the period indicates the value of:

Give a brief account of the counter current mechanism.

Which of the following statements related to the modern periodic table is incorrect?

Draw a standard ECG and explain the different segments in it.

What is K_c for the following equilibrium when the equilibrium concentration of each substance is: [SO₂]= 0.60 M, [O₂] = 0.82 M and [SO₃] = 1.90 M ?
\(2SO_2(g) + O_2(g) ⇋ 2SO_3(g)\)

Which one of the following statements is incorrect in relation to ionization enthalpy?

Considering the elements B, Al, Mg, and K, the correct order of their metallic character is:

Considering the elements B, C, N, F, and Si, the correct order of their non-metallic character is:

At a certain temperature and total pressure of 10⁵ Pa, iodine vapour contains 40% by volume of \(\text {I}\) atoms
\( I_2 (g) ⇋ 2I (g)\)
Calculate K_p for the equilibrium.

Describe the evolutionary change in the pattern of heart among the vertebrates.

Distinguish cytokinesis from karyokinesis.

Considering the elements F, Cl, O and N, the correct order of their chemical reactivity in terms of oxidizing property is:

How does cytokinesis in plant cells differ from that in animal cells?

Write the expression for the equilibrium constant, K_c 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. \(I_2 (s) + 5F_2 ⇋ 2IF_5\)

Define octet rule. Write its significance and limitations.

Discuss the shape of the following molecules using the VSEPR model: 
BeCl₂, BCl₃, SiCl₄, AsF₅, H₂S, PH₃

Although geometries of NH₃ and H₂O molecules are distorted tetrahedral, bond angle in water is less than that of ammonia. Discuss.

Explain the important aspects of resonance with reference to the \(CO_3^{2-}\) ion.

H₃PO₃ can be represented by structures 1 and 2 shown below. Can these two structures be taken as the canonical forms of the resonance hybrid representing H₃PO₃ ? If not, give reasons for the same.

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. \(CaCO_3 (s) ⇋ CaO(s) + CO_2(g); \ K_p= 167 \ at \ 1073\  K\)

What is the difference between lymph and blood?