NBSE Class 11 Question Paper 2021 for Chemistry

Total number of printed pages : 3 NB/XI/CHE/1
2021
CHEMISTRY
Total marks : 70 Time : 3 hours

General instructions:
i) Approximately 15 minutes is allotted to read the question paper and revise the
answers.
ii) The question paper consists of 30 questions. All questions are compulsory.
iii) Marks are indicated against each question.
 iv) Internal choice has been provided in some questions.

N.B: Check that all pages of the question paper is complete as indicated on the top left side.

1. Which of the following has the highest electronegativity? 1
(a) Li (b) Be (c) B (d) C

2. Boyle’s law states that 1
1
(a) V α T (b) P α (c) P α T (d) V  n
V

3. For the process to occur under adiabatic condition, the correct condition is 1
(a) ∆T=0 (b) ΔP=0 (c) q = 0 (d) W = 0

4. During oxidation, the oxidation number of element 1
(a) increases (b) decreases
(c) does not change (d) unpredictable.

5. In group – 14, the inert pair effect is most prominent in 1
(a) tin and lead (b) carbon and silicon
(c) silicon and germanium (d) all of them.

6. State the law of multiple proportions. 1

7. Write the general electronic configuration of d – block elements. 1

8. State Dalton’s law of partial pressure. 1

9. Define standard enthalpy of formation. 1

10. State Bronsted – Lowry concept of acids and bases. 1

-2- NB/XI/CHE/1

11. a. Calculate the molarity of NaOH in the solution prepared by dissolving
its 4g in enough water to form 250 ml of the solution.
Or 2
b. Calculate the percentage composition of C, H and O in C 2H5OH.

12. What is electronic configuration? Write the electronic configuration
of Cr. 2

13. a. Draw the boundary surface diagrams of the three 2p orbital.
Or 2
b. A microscope using suitable photons is employed to locate an
electron in an atom within a distance of 0.1Ǻ. What is the
uncertainty involved in the measurement of its velocity?

14. Define octet rule. Draw the Lewis dot structure of C2H2. 2

15. Write one preparation of hydrogen peroxide. Give one use. 2

16. a. Explain the amphoteric nature of water.
Or 2
b. Write the treatment of temporary hardness of water by Clark’s
method.

17. a. What are the frequency and wavelength of a photon emitted during
a transition from n=5 state to the n=2 state in the hydrogen atom?
Or 3
b. What are quantum numbers? Explain the four types of quantum
numbers.

18. What is atomic radius? How does it vary across a group and period in a
periodic table? 3

19. A neon-dioxygen mixture contains 70.6g dioxygen and 167.5g neon,
if pressure of the mixture of gas in the cylinder is 25 bar. What is the
partial pressure of dioxygen and neon in the mixture? 3

20. The value of Kc= 4.24 at 800K for the reaction:
CO(g) + H2O(g) CO2(g) + H2(g). Calculate the equilibrium
concentration of CO2,H2,CO and H2O at 800K, if only CO and H2O are
present initially at concentration of 0.10M each. 3

21. a. What is buffer solution? Write the expression by Henderson – Hasselbalch
equation where the weak acid HA ionizes in water.
b. What is meant by homogenous equilibria and heterogenous equilibria?
Give one example each.

-3- NB/XI/CHE/1

22. a. Write the net ionic equation for the reaction of potassium dichromate
(VI) K2Cr2O7 with sodium sulphate Na2SO3 in an acid solution to give
chromium (III) ion and the sulphate ion.
b. What is displacement reaction? Explain the type of displacement
reaction.

23. Why do lithium behaves differently from other alkali metals? Give reasons. 3

24. a. Explain the properties of atomic and ionic radii and ionization
enthalpy in alkali metals.
Or 3
b. Write the preparation of calcium sulphate. Give one use.

25. Give reasons why: 3
3
(a) boron is unstable to form BF6 ion.
(b) white fumes appear around the bottle of anhydrous aluminium chloride.
(c) diamond is covalent, yet it have high melting point.

26. What are producer gas and water gas? Give reaction. 3

27. Explain the acidic character of alkyne. 3

28. a. What is hybridization? Draw the structure and mention the type of
hybridization in PCl5, SF6 and NH3 .
Or 5
b. Compare the relative stability of O2 , O2 and O2 on the basis of
molecular orbital theory.

29. a. Define entropy. A swimmer coming out from a pool is covered with
a film of water weighing about 18g. How much heat must be supplied to
evaporate this water at 298K. Calculate the internal energy of
vaporization at 298K.
Or 5
b. Calculate the lattice enthalpy of Na+Cl− by Born Haber cycle.

30. a. (i) Explain Markovnikov rule and anti-Markovnikov rule with reaction.
(ii) Give the IUPAC name of CH3CH2CHOHCH2CH3.
Or 5
b. What are conformers? Explain the conformation of ethane for
Sawhorse projections and Newman projections.

**********************