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Some Basic Concepts of Chemistry JEE Main MCQ & Practice Questions

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

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Some Basic Concepts of Chemistry Revision Guide for JEE Main Chemistry

Some Basic Concepts of Chemistry is part of JEE Main 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

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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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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.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

1. One mole of any substance contains:

  • A. 1.0 × 10^3 entities
  • B. 3.011 × 10^23 entities
  • C. 6.022 × 10^23 entities
  • D. 22.4 entities
Answer: C
Explanation: One mole contains Avogadro's number, 6.022 × 10^23 entities.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

2. The molar mass of CO2 is:

  • A. 18 g mol−1
  • B. 44 g mol−1
  • C. 28 g mol−1
  • D. 32 g mol−1
Answer: B
Explanation: CO2 has molar mass 12 + 2×16 = 44 g mol−1.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

3. The number of moles in 11 g CO2 is:

  • A. 0.25 mol
  • B. 0.50 mol
  • C. 1.00 mol
  • D. 2.00 mol
Answer: A
Explanation: Moles = 11/44 = 0.25 mol.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

4. The number of molecules in 0.50 mol O2 is:

  • A. 6.022 × 10^23
  • B. 1.204 × 10^24
  • C. 1.505 × 10^23
  • D. 3.011 × 10^23
Answer: D
Explanation: Molecules = 0.50×6.022×10^23 = 3.011×10^23.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

5. The number of oxygen atoms in 0.25 mol O2 is:

  • A. 6.022 × 10^23
  • B. 1.204 × 10^24
  • C. 3.011 × 10^23
  • D. 1.505 × 10^23
Answer: C
Explanation: 0.25 mol O2 contains 0.50 mol O atoms, equal to 3.011×10^23 atoms.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

6. The empirical formula of a compound containing 40% C, 6.67% H and 53.33% O is:

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

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

7. If empirical formula is CH2O and molar mass is 180 g mol−1, molecular formula is:

  • A. C6H12O6
  • B. C3H6O3
  • C. CH2O
  • D. C2H4O2
Answer: A
Explanation: Empirical formula mass = 30; multiplier = 180/30 = 6.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

8. For N2 + 3H2 → 2NH3, 2 mol N2 requires:

  • A. 3 mol H2
  • B. 2 mol H2
  • C. 1 mol H2
  • D. 6 mol H2
Answer: D
Explanation: Stoichiometric ratio N2:H2 is 1:3.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

9. For N2 + 3H2 → 2NH3, 3 mol H2 can form:

  • A. 3 mol NH3
  • B. 6 mol NH3
  • C. 2 mol NH3
  • D. 1 mol NH3
Answer: C
Explanation: Three moles H2 produce two moles NH3.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

10. If 2 mol N2 reacts with 3 mol H2, the limiting reagent is:

  • A. Neither
  • B. H2
  • C. N2
  • D. NH3
Answer: B
Explanation: 2 mol N2 needs 6 mol H2, but only 3 mol is available.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

11. Percentage yield is calculated as:

  • A. Actual yield/theoretical yield × 100
  • B. Theoretical yield/actual yield × 100
  • C. Actual yield × theoretical yield
  • D. Actual yield − theoretical yield
Answer: A
Explanation: Percentage yield compares actual product with theoretical maximum.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

12. A 20 g sample that is 80% pure contains pure substance equal to:

  • A. 4 g
  • B. 20 g
  • C. 25 g
  • D. 16 g
Answer: D
Explanation: Pure mass = 20×0.80 = 16 g.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

13. Molarity is defined as:

  • A. Mass of solute per litre solvent
  • B. Moles of solvent per litre solution
  • C. Moles of solute per litre of solution
  • D. Moles of solute per kg solvent
Answer: C
Explanation: Molarity is n/Vsolution in litres.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

14. Molality is defined as:

  • A. Moles of solvent per litre
  • B. Moles of solute per kg solvent
  • C. Moles of solute per litre solution
  • D. Mass of solute per kg solution
Answer: B
Explanation: Molality uses kilograms of solvent.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

15. Which concentration term is temperature independent?

  • A. Molality
  • B. Molarity
  • C. Normality based on volume
  • D. Volume percent
Answer: A
Explanation: Molality depends on masses, not volume.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

16. Mole fraction is:

  • A. Measured in mol L−1
  • B. Measured in mol kg−1
  • C. Measured in grams
  • D. Dimensionless
Answer: D
Explanation: It is a ratio of moles to total moles.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

17. At STP, one mole of an ideal gas occupies approximately:

  • A. 44.8 L
  • B. 1.0 L
  • C. 22.4 L
  • D. 11.2 L
Answer: C
Explanation: The molar volume at STP is approximately 22.4 L mol−1.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

18. The law stating that mass is neither created nor destroyed is:

  • A. Boyle's law
  • B. Law of conservation of mass
  • C. Law of multiple proportions
  • D. Avogadro's law
Answer: B
Explanation: Total mass remains constant in a closed chemical reaction.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

19. When two elements form more than one compound, masses combining with a fixed mass are in simple whole-number ratios. This is:

  • A. Law of multiple proportions
  • B. Law of constant composition
  • C. Law of conservation of mass
  • D. Gay-Lussac's law
Answer: A
Explanation: This is the law of multiple proportions.

JEE Main Chemistry · Some Basic Concepts of Chemistry · Very Hard

20. The number of significant figures in 0.004560 is:

  • A. 3
  • B. 5
  • C. 2
  • D. 4
Answer: D
Explanation: Leading zeros are not significant; trailing decimal zeros are significant.

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Some Basic Concepts of Chemistry Frequently Asked Questions

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