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Some Basic Concepts of Chemistry WBCHSE Class 11 MCQ & Practice Questions

Practice Some Basic Concepts of Chemistry MCQs for WBCHSE Class 11 Chemistry with answers, explanations, chapter revision and related ChemNexa mock tests.

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Some Basic Concepts of Chemistry Revision Guide for WBCHSE Class 11 Chemistry

Some Basic Concepts of Chemistry is part of WBCHSE Class 11 Chemistry preparation. A strong revision plan should combine concept review with exam-style questions so that definitions, relationships, calculations and exceptions are recalled accurately.

Use the sample MCQs on this page to check understanding, then attempt the related ChemNexa tests for broader practice. When an answer is wrong, review the explanation and return to the underlying concept before attempting another set.

Important Topics

  • Core definitions and principles
  • Important equations or relationships
  • Common applications and examples
  • Frequently confused concepts
  • Exam-style multiple-choice questions
  • Error review and targeted revision

Revision Tip

Create a one-page summary of trends, structures, reactions, exceptions and key terminology for Some Basic Concepts of Chemistry, then test recall with mixed MCQs.

What to practise in Some Basic Concepts of Chemistry

Concept Revision

Revise definitions, principles, equations, trends and core ideas from Some Basic Concepts of Chemistry before attempting MCQs.

Exam-style MCQs

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Performance Practice

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Top 20 Some Basic Concepts of Chemistry MCQs with Answers

These public questions are selected from the exact Some Basic Concepts of Chemistry chapter, screened for topic relevance and deduplicated so repeated versions of the same MCQ are not shown publicly. Use them for quick revision, then sign in to attempt the complete test experience with more questions, results and performance review.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

1. The law of conservation of mass was formulated by:

  • A. Dalton
  • B. Avogadro
  • C. Lavoisier
  • D. Proust
Answer: C
Explanation: Lavoisier established that mass is conserved during a chemical reaction.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

2. The law of definite proportions was proposed by:

  • A. Rutherford
  • B. Proust
  • C. Lavoisier
  • D. Gay-Lussac
Answer: B
Explanation: Proust stated that a pure compound always contains the same elements in a fixed mass ratio.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

3. If two elements form more than one compound, the masses of one combining with a fixed mass of the other are in simple whole-number ratios. This is:

  • A. Law of multiple proportions
  • B. Law of conservation of mass
  • C. Avogadro law
  • D. Boyle law
Answer: A
Explanation: Dalton's law of multiple proportions describes simple whole-number mass ratios.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

4. One atomic mass unit is defined as:

  • A. Mass of one hydrogen atom exactly
  • B. 1/16 mass of oxygen-16
  • C. Mass of one electron
  • D. 1/12 mass of one carbon-12 atom
Answer: D
Explanation: The unified atomic mass unit is one-twelfth the mass of a carbon-12 atom.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

5. One mole contains approximately:

  • A. 9.11×10^-31 entities
  • B. 1.66×10^-27 entities
  • C. 6.022×10^23 entities
  • D. 3.011×10^23 entities
Answer: C
Explanation: Avogadro constant is approximately 6.022×10^23 mol^-1.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

6. The number of moles in 18 g of water is:

  • A. 18
  • B. 1
  • C. 2
  • D. 0.5
Answer: B
Explanation: Molar mass of H2O is 18 g mol^-1, so n=18/18=1 mol.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

7. The number of molecules in 0.5 mol O2 is:

  • A. 3.011×10^23
  • B. 6.022×10^23
  • C. 1.2044×10^24
  • D. 0.5
Answer: A
Explanation: Number of molecules = 0.5×NA = 3.011×10^23.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

8. The molar mass of CO2 is approximately:

  • A. 28 g mol^-1
  • B. 32 g mol^-1
  • C. 18 g mol^-1
  • D. 44 g mol^-1
Answer: D
Explanation: 12 + 2×16 = 44 g mol^-1.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

9. The mass of 0.25 mol NaOH is:

  • A. 20 g
  • B. 5 g
  • C. 10 g
  • D. 40 g
Answer: C
Explanation: Molar mass NaOH=40 g mol^-1; mass=0.25×40=10 g.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

10. How many moles are present in 11 g CO2?

  • A. 4 mol
  • B. 0.25 mol
  • C. 0.5 mol
  • D. 1 mol
Answer: B
Explanation: n=m/M=11/44=0.25 mol.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

11. The percentage by mass of oxygen in water is approximately:

  • A. 88.9%
  • B. 11.1%
  • C. 50%
  • D. 16%
Answer: A
Explanation: Oxygen contributes 16 of 18 mass units: 16/18×100≈88.9%.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

12. An empirical formula represents:

  • A. Actual number of atoms always
  • B. Molecular mass
  • C. Only ionic charge
  • D. Simplest whole-number ratio of atoms
Answer: D
Explanation: The empirical formula gives the simplest integral atomic ratio.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

13. Molecular formula is related to empirical formula by:

  • A. They are never related
  • B. Molecular formula = molar mass only
  • C. Molecular formula = n × empirical formula
  • D. Molecular formula = empirical formula/n
Answer: C
Explanation: The molecular formula is an integral multiple of the empirical formula.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

14. If empirical formula mass is 30 and molar mass is 60, n equals:

  • A. 0.5
  • B. 2
  • C. 1
  • D. 3
Answer: B
Explanation: n = molar mass/empirical formula mass = 60/30 = 2.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

15. A compound contains 40% C, 6.67% H and 53.33% O. Its empirical formula is:

  • A. CH2O
  • B. C2H4O2
  • C. CHO
  • D. CH3O
Answer: A
Explanation: For 100 g: C=3.33 mol, H=6.67 mol, O=3.33 mol, giving 1:2:1.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

16. Stoichiometry deals with:

  • A. Only reaction mechanisms
  • B. Only colour changes
  • C. Only atomic spectra
  • D. Quantitative relationships in chemical reactions
Answer: D
Explanation: Stoichiometry uses balanced equations to relate amounts of reactants and products.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

17. In 2H2 + O2 -> 2H2O, moles of H2 required for 1 mol O2 are:

  • A. 0.5
  • B. 4
  • C. 2
  • D. 1
Answer: C
Explanation: The balanced equation gives H2:O2 = 2:1.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

18. In N2 + 3H2 -> 2NH3, 1 mol N2 ideally forms:

  • A. 0.5 mol NH3
  • B. 2 mol NH3
  • C. 1 mol NH3
  • D. 3 mol NH3
Answer: B
Explanation: Stoichiometric coefficients give 1 mol N2 to 2 mol NH3.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

19. The limiting reagent is the reactant that:

  • A. Is consumed first and limits product amount
  • B. Has the greatest molar mass
  • C. Is always present in excess
  • D. Acts as catalyst
Answer: A
Explanation: The limiting reagent determines the maximum theoretical product.

WBCHSE Class 11 Chemistry · Some Basic Concepts of Chemistry · Very Hard

20. If 2 mol H2 react with 2 mol O2 according to 2H2+O2->2H2O, the limiting reagent is:

  • A. O2
  • B. H2O
  • C. Neither
  • D. H2
Answer: D
Explanation: 2 mol H2 require only 1 mol O2, so H2 is consumed first.

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