MCQs on Some Basic Concepts of Chemistry – Class 11 Chemistry
MCQs on Some Basic Concepts of Chemistry – Class 11 Chemistry
Course: CBSE Class 11 Chemistry – MCQs with Answers and Explanations
Section: Physical Chemistry – MCQ Titles
The following 50 NCERT-based MCQs are strictly aligned with the CBSE Class 11 syllabus. Questions are organized section-wise by concepts, and each MCQ includes the correct answer with a clear, concept-clearing explanation, making them ideal for board exam preparation and revision.
Section A: Nature and Scope of Chemistry
1. Chemistry is best defined as the study of
A. living organisms
B. matter and energy
C. matter, its properties, and transformations
D. chemical industries
Answer: C
Explanation: Chemistry deals with matter, its composition, structure, properties, and the changes it undergoes.
2. Which branch of chemistry studies the rate of chemical reactions?
A. Thermodynamics
B. Kinetics
C. Electrochemistry
D. Stoichiometry
Answer: B
Explanation: Chemical kinetics focuses on reaction rates and factors affecting them.
Section B: Laws of Chemical Combination
3. Law of conservation of mass was proposed by
A. Dalton
B. Lavoisier
C. Proust
D. Gay-Lussac
Answer: B
Explanation: Lavoisier stated that mass is neither created nor destroyed in a chemical reaction.
4. The law of definite proportions states that
A. elements combine in any ratio
B. mass is conserved
C. a compound has fixed composition by mass
D. gases combine in volumes
Answer: C
Explanation: A given compound always contains the same elements in the same mass ratio.
5. Which law supports the formation of multiple compounds?
A. Conservation of mass
B. Definite proportions
C. Multiple proportions
D. Reciprocal proportions
Answer: C
Explanation: The law of multiple proportions explains formation of more than one compound by same elements.
Section C: Atomic and Molecular Masses
6. Atomic mass is expressed relative to
A. hydrogen atom
B. oxygen atom
C. carbon-12 atom
D. helium atom
Answer: C
Explanation: Atomic masses are compared relative to 1/12th the mass of carbon-12.
7. Molecular mass of H₂SO₄ is
A. 96 u
B. 98 u
C. 100 u
D. 102 u
Answer: B
Explanation: (2×1) + 32 + (4×16) = 98 u.
8. The unit of atomic mass is
A. kg
B. g
C. amu or u
D. mole
Answer: C
Explanation: Atomic mass unit (u) is used to express atomic masses.
Section D: Mole Concept
9. One mole of a substance contains
A. 6.022 × 10¹⁹ particles
B. 6.022 × 10²² particles
C. 6.022 × 10²³ particles
D. 6.022 × 10²⁶ particles
Answer: C
Explanation: Avogadro’s number represents particles in one mole.
10. Number of moles in 18 g of water is
A. 0.5
B. 1
C. 2
D. 18
Answer: B
Explanation: Moles = mass / molar mass = 18 / 18 = 1 mole.
11. Which quantity represents amount of substance?
A. Mass
B. Volume
C. Mole
D. Density
Answer: C
Explanation: Mole is the SI unit of amount of substance.
12. Number of atoms in 1 mole of sodium is
A. 11
B. 23
C. 6.022 × 10²³
D. 3.011 × 10²³
Answer: C
Explanation: One mole of any element contains Avogadro’s number of atoms.
Section E: Percentage Composition
13. Percentage composition refers to
A. mass of compound
B. volume of compound
C. mass percentage of each element
D. atomic mass
Answer: C
Explanation: It indicates the mass contribution of each element in a compound.
14. Percentage of hydrogen in water is approximately
A. 5.56%
B. 11.11%
C. 33.33%
D. 88.89%
Answer: B
Explanation: (2/18) × 100 = 11.11%.
Section F: Empirical and Molecular Formula
15. Empirical formula represents
A. actual number of atoms
B. simplest whole number ratio
C. molar mass
D. percentage composition
Answer: B
Explanation: It gives the simplest ratio of atoms in a compound.
16. Molecular formula of a compound is always
A. same as empirical formula
B. double of empirical formula
C. multiple of empirical formula
D. unrelated to empirical formula
Answer: C
Explanation: Molecular formula is an integral multiple of empirical formula.
17. Empirical formula of glucose (C₆H₁₂O₆) is
A. CH₂O
B. C₂H₄O₂
C. C₃H₆O₃
D. C₆H₁₂O₆
Answer: A
Explanation: Simplest ratio is obtained by dividing subscripts by 6.
Section G: Stoichiometry
18. Stoichiometry deals with
A. reaction rates
B. mass–volume relationships
C. quantitative relationships in reactions
D. chemical equilibrium
Answer: C
Explanation: It involves calculation of reactants and products.
19. Limiting reagent is the reactant
A. present in excess
B. with highest molar mass
C. consumed first
D. least reactive
Answer: C
Explanation: It limits the amount of product formed.
20. The reactant left after reaction is called
A. limiting reagent
B. catalyst
C. excess reagent
D. product
Answer: C
Explanation: Excess reagent remains unreacted.
Section H: Concentration of Solutions
21. Molarity is defined as
A. moles per kg solvent
B. moles per litre of solution
C. grams per litre
D. percentage by mass
Answer: B
Explanation: Molarity (M) = moles of solute / volume of solution (L).
22. Molality is independent of
A. mass
B. temperature
C. moles
D. solvent
Answer: B
Explanation: Molality depends on mass, not volume, hence temperature independent.
23. Normality is expressed as
A. equivalents per litre
B. moles per litre
C. grams per litre
D. moles per kg
Answer: A
Explanation: Normality is based on equivalents of solute.
Section I: Numerical & Conceptual Applications
24. SI unit of density is
A. g cm⁻³
B. kg m⁻³
C. g L⁻¹
D. kg L⁻¹
Answer: B
Explanation: Density = mass/volume in SI units.
25. Which quantity remains constant in a chemical reaction?
A. Volume
B. Temperature
C. Pressure
D. Mass
Answer: D
Explanation: According to conservation of mass, mass remains constant.
Section I: Numerical & Conceptual Applications (Continued)
26. How many moles of CO₂ are present in 44 g of CO₂?
A. 0.5
B. 1
C. 2
D. 44
Answer: B
Explanation: Moles = mass ÷ molar mass = 44 ÷ 44 = 1 mole.
27. Number of molecules present in 2 moles of oxygen gas is
A. 6.022 × 10²³
B. 1.204 × 10²⁴
C. 3.011 × 10²³
D. 12.044 × 10²³
Answer: B
Explanation: Molecules = moles × Avogadro’s number = 2 × 6.022 × 10²³.
28. Which of the following contains the maximum number of atoms?
A. 1 mole of H₂
B. 1 mole of O₂
C. 1 mole of N₂
D. 1 mole of He
Answer: A
Explanation: H₂ has 2 atoms per molecule, so total atoms = 2 moles of atoms.
29. The number of moles of solute present in 500 mL of a 2 M solution is
A. 0.5
B. 1
C. 2
D. 4
Answer: B
Explanation: Moles = M × volume (L) = 2 × 0.5 = 1 mole.
30. Which concentration unit changes with temperature?
A. Molality
B. Mole fraction
C. Molarity
D. Mass percentage
Answer: C
Explanation: Molarity depends on volume, which varies with temperature.
Section J: Stoichiometric Calculations
31. How many grams of NaCl are present in 0.5 mole of NaCl?
A. 29.25 g
B. 58.5 g
C. 14.6 g
D. 117 g
Answer: A
Explanation: Mass = moles × molar mass = 0.5 × 58.5 = 29.25 g.
32. If 2 moles of hydrogen react with oxygen, how many moles of water are formed?
A. 1
B. 2
C. 3
D. 4
Answer: B
Explanation: Balanced equation: 2H₂ + O₂ → 2H₂O.
33. The limiting reagent in a reaction is the substance that
A. has minimum mass
B. is least reactive
C. is completely consumed
D. remains unreacted
Answer: C
Explanation: Limiting reagent gets used up first and limits product formation.
34. Which of the following is NOT a stoichiometric calculation?
A. Mole to mass conversion
B. Reactant to product calculation
C. Rate of reaction calculation
D. Percentage yield calculation
Answer: C
Explanation: Reaction rate belongs to chemical kinetics.
Section K: Concentration Terms
35. Molality is defined as moles of solute per
A. litre of solution
B. litre of solvent
C. kg of solution
D. kg of solvent
Answer: D
Explanation: Molality = moles of solute / kg of solvent.
36. The unit of molality is
A. mol L⁻¹
B. mol kg⁻¹
C. g L⁻¹
D. g kg⁻¹
Answer: B
Explanation: Molality is expressed as moles per kilogram.
37. Which of the following is a dimensionless quantity?
A. Molarity
B. Molality
C. Mole fraction
D. Normality
Answer: C
Explanation: Mole fraction is a ratio and has no units.
38. A solution containing 10 g solute in 100 g solution has mass percentage of
A. 5%
B. 10%
C. 20%
D. 90%
Answer: B
Explanation: (10 ÷ 100) × 100 = 10%.
Section L: Conceptual NCERT-Based MCQs
39. Which quantity represents the chemical amount of a substance?
A. Mass
B. Volume
C. Mole
D. Density
Answer: C
Explanation: Mole is the SI unit for amount of substance.
40. Avogadro number is applicable to
A. atoms only
B. molecules only
C. ions only
D. all particles
Answer: D
Explanation: It applies to atoms, molecules, ions, electrons, etc.
41. The molar mass of a compound is numerically equal to its
A. atomic mass
B. molecular mass
C. equivalent mass
D. density
Answer: B
Explanation: Molecular mass in u equals molar mass in g mol⁻¹.
42. Which of the following laws explains the fixed composition of compounds?
A. Law of multiple proportions
B. Law of conservation of mass
C. Law of definite proportions
D. Gay-Lussac’s law
Answer: C
Explanation: It states that a compound always contains same elements in same mass ratio.
43. Which of the following is NOT a state function?
A. Pressure
B. Temperature
C. Volume
D. Path length
Answer: D
Explanation: Path length depends on the route taken, not the state.
44. The empirical formula mass of a compound is always
A. equal to molecular mass
B. greater than molecular mass
C. less than or equal to molecular mass
D. unrelated to molecular mass
Answer: C
Explanation: Molecular mass is a whole number multiple of empirical mass.
45. A balanced chemical equation obeys
A. law of multiple proportions
B. law of conservation of mass
C. law of reciprocal proportions
D. Gay-Lussac’s law
Answer: B
Explanation: Number of atoms of each element remains same on both sides.
46. Which of the following is used to express very small masses of atoms?
A. gram
B. kilogram
C. atomic mass unit
D. mole
Answer: C
Explanation: Atomic mass unit (u) is suitable for atomic-scale masses.
47. The formula unit mass is used for
A. covalent compounds
B. molecular substances
C. ionic compounds
D. gases only
Answer: C
Explanation: Ionic compounds do not exist as discrete molecules.
48. The term stoichiometry was introduced by
A. Dalton
B. Ostwald
C. Richter
D. Lavoisier
Answer: C
Explanation: Richter introduced the term stoichiometry.
49. Which of the following has the highest molar mass?
A. CO₂
B. N₂
C. O₂
D. CH₄
Answer: A
Explanation: CO₂ = 44 g mol⁻¹, highest among given options.
50. Which calculation is most useful in predicting product yield?
A. Empirical formula
B. Limiting reagent
C. Atomic mass
D. Mole fraction
Answer: B
Explanation: Limiting reagent determines maximum amount of product formed.
✅ Completion Note
With this, the full set of 50 MCQs on Some Basic Concepts of Chemistry is complete, fully NCERT-aligned, CBSE-ready, and ideal for concept clarity, numericals, and exam preparation.