Class 11 – Some Basic Concepts of Chemistry (50 MCQs)
Basic Definitions & Concepts (1–8)
- Which of the following represents a molecule?
a) NaCl
b) O₂
c) K
d) Fe - The smallest particle of an element that retains its chemical properties is:
a) Atom
b) Molecule
c) Ion
d) Electron - Which of the following is a chemical formula?
a) H₂O
b) H₂O (liquid)
c) Water
d) Hydrogen - Avogadro’s number is:
a) 6.022 × 10²³
b) 6.022 × 10²²
c) 1.602 × 10⁻¹⁹
d) 3.0 × 10⁸ - Which of the following statements is true about a molecule?
a) It can exist independently
b) It always contains two or more elements
c) It is a charged particle
d) It is smaller than an atom - Which of the following is a compound?
a) O₂
b) H₂O
c) N₂
d) Cl₂ - The SI unit of amount of substance is:
a) Gram
b) Mole
c) Liter
d) Kilogram - Which of these is NOT a chemical change?
a) Rusting of iron
b) Melting of ice
c) Burning of paper
d) Digestion of food
Atomic & Molecular Mass, Molar Mass (9–16)
- The molar mass of CO₂ is approximately:
a) 44 g/mol
b) 28 g/mol
c) 32 g/mol
d) 12 g/mol - Atomic mass of an element is:
a) Mass of 1 mole of the element
b) Mass of one atom in atomic mass units
c) Mass of 1 liter of the element
d) None of the above - Which element has an atomic mass closest to 40 u?
a) Ca
b) K
c) Ar
d) Cl - The molecular mass of H₂SO₄ is:
a) 98 u
b) 100 u
c) 96 u
d) 102 u - Which of the following has the highest molar mass?
a) H₂O
b) CO₂
c) C₆H₁₂O₆
d) NaCl - 1 mole of oxygen atoms contains:
a) 6.022 × 10²³ atoms
b) 12 g atoms
c) 22.4 L
d) 16 g - The molar mass of a substance is numerically equal to:
a) Its atomic mass
b) Its molecular mass in grams
c) Its molecular mass in kg
d) Its density - The relative molecular mass of NH₃ is:
a) 17
b) 16
c) 14
d) 18
Stoichiometry & Chemical Equations (17–26)
- In the reaction: 2H₂ + O₂ → 2H₂O, the ratio of H₂ : H₂O is:
a) 1 : 1
b) 2 : 2
c) 2 : 1
d) 1 : 2 - In the reaction: N₂ + 3H₂ → 2NH₃, 1 mole of N₂ reacts with how many moles of H₂?
a) 1
b) 2
c) 3
d) 4 - Which of the following reactions represents the Law of Conservation of Mass?
a) H₂ + Cl₂ → 2HCl
b) Na + H₂O → NaOH + H₂
c) CaCO₃ → CaO + CO₂
d) All of the above - How many grams of water are formed when 4 g of hydrogen reacts with excess oxygen? (Molar mass H = 1, O = 16)
a) 36 g
b) 32 g
c) 18 g
d) 8 g - 44 g of CO₂ contains how many moles of carbon?
a) 1
b) 2
c) 0.5
d) 4 - If 3 moles of H₂ react with N₂ to form NH₃, how many moles of NH₃ are produced?
a) 1
b) 2
c) 3
d) 6 - Which of the following is the correct stoichiometric ratio in the combustion of CH₄: CH₄ + 2O₂ → CO₂ + 2H₂O?
a) CH₄ : O₂ = 1 : 1
b) CH₄ : O₂ = 1 : 2
c) CH₄ : CO₂ = 2 : 1
d) CH₄ : H₂O = 1 : 2 - In the reaction 2Al + 3Cl₂ → 2AlCl₃, 54 g of Al reacts with chlorine. How many grams of AlCl₃ will form? (Al = 27, Cl = 35.5)
a) 135 g
b) 162 g
c) 108 g
d) 243 g - Which is a limiting reagent problem?
a) Given amounts of two reactants and asked which runs out first
b) Balancing equations
c) Finding molecular mass
d) Converting grams to moles - How many moles of oxygen are required to completely react with 6 moles of CH₄?
a) 6
b) 12
c) 18
d) 24
Laws of Chemical Combination (27–33)
- Law of Definite Proportions was proposed by:
a) Dalton
b) Proust
c) Lavoisier
d) Avogadro - Which law states “mass is neither created nor destroyed in a chemical reaction”?
a) Law of Multiple Proportions
b) Law of Conservation of Mass
c) Law of Definite Proportions
d) Avogadro’s Law - Dalton’s Law of Multiple Proportions is applicable when:
a) Two elements form more than one compound
b) Two elements form a single compound
c) Any reaction occurs
d) None of the above - 2 g of H combine with 16 g of O to form water. Which law is illustrated?
a) Law of Conservation of Mass
b) Law of Multiple Proportions
c) Law of Definite Proportions
d) Avogadro’s Law - 12 g of C combines with 32 g of O to form CO₂. Which law is illustrated?
a) Law of Conservation of Mass
b) Law of Definite Proportions
c) Law of Multiple Proportions
d) Avogadro’s Law - When two elements combine in different ratios to form different compounds, the ratio of masses is:
a) Simple fraction
b) Decimal fraction
c) Always 1:1
d) Variable - Which scientist’s work laid the foundation for the concept of atomic theory?
a) Proust
b) Lavoisier
c) Dalton
d) Avogadro
Empirical & Molecular Formula (34–41)
- A compound contains 40% C, 6.7% H, and 53.3% O. Its empirical formula is:
a) CH₂O
b) C₂H₄O₂
c) CHO
d) C₂HO - Molecular formula = n × empirical formula. If molar mass = 180 g/mol and empirical formula mass = 30 g/mol, n = ?
a) 5
b) 6
c) 4
d) 3 - A compound has empirical formula CH₂O. Its molecular mass is 60 g/mol. Molecular formula is:
a) CH₂O
b) C₂H₄O₂
c) C₃H₆O₃
d) C₄H₈O₄ - Empirical formula gives information about:
a) Actual number of atoms
b) Ratio of atoms
c) Molar mass
d) Density - Which formula represents the actual number of atoms in a molecule?
a) Empirical formula
b) Molecular formula
c) Structural formula
d) Ionic formula - Molecular formula of glucose is C₆H₁₂O₆. Its empirical formula is:
a) CH₂O
b) C₃H₆O₃
c) C₆H₁₂O₆
d) CHO - Percentage composition is based on:
a) Mass of each element per mole
b) Number of atoms
c) Volume of compound
d) Mass of one atom - If a compound has empirical formula CH and molar mass 78 g/mol, molecular formula is:
a) C₆H₆
b) C₇H₇
c) C₅H₅
d) CH
Percentage Composition & Miscellaneous (42–50)
- In H₂O, percentage of H is approximately:
a) 11%
b) 2%
c) 22%
d) 88% - 1 mole of NaCl weighs:
a) 58.5 g
b) 35.5 g
c) 23 g
d) 40 g - Which is NOT correct for the mole concept?
a) 1 mole of any substance contains 6.022 × 10²³ particles
b) Mole is a counting unit
c) 1 mole of H₂O weighs 18 kg
d) Mole can refer to atoms, molecules, or ions - The mass ratio of H:O in water is:
a) 1:8
b) 1:16
c) 2:16
d) 1:1 - Which is the correct representation of 1 mole of oxygen gas at STP?
a) 6.022 × 10²³ O₂ molecules
b) 6.022 × 10²³ O atoms
c) 22.4 g of O₂
d) Both a & c - The number of moles in 88 g of CO₂ (M = 44 g/mol) is:
a) 1
b) 2
c) 3
d) 4 - Which of the following is a limiting reagent problem?
a) Given 5 g H₂ reacts with 40 g O₂ to form water
b) 2H₂ + O₂ → 2H₂O
c) Calculation of molecular mass
d) Determining empirical formula - The mass of 1 mole of H₂SO₄ is:
a) 98 g
b) 100 g
c) 96 g
d) 102 g - Which of the following statements is TRUE?
a) Mole is the SI unit of mass
b) Empirical formula always equals molecular formula
c) Stoichiometry deals with quantitative relationships in chemical reactions
d) Atomic mass and molar mass are identical numerically and in units
Answer Key – Class 11 Chemistry: Some Basic Concepts of Chemistry
Basic Definitions & Concepts (1–8)
- b) O₂
- a) Atom
- a) H₂O
- a) 6.022 × 10²³
- a) It can exist independently
- b) H₂O
- b) Mole
- b) Melting of ice
Atomic & Molecular Mass, Molar Mass (9–16)
- a) 44 g/mol
- b) Mass of one atom in atomic mass units
- a) Ca
- a) 98 u
- c) C₆H₁₂O₆
- a) 6.022 × 10²³ atoms
- b) Its molecular mass in grams
- a) 17
Stoichiometry & Chemical Equations (17–26)
- b) 2 : 2
- c) 3
- d) All of the above
- a) 36 g
- a) 1
- b) 2
- b) CH₄ : O₂ = 1 : 2
- b) 162 g
- a) Given amounts of two reactants and asked which runs out first
- b) 12
Laws of Chemical Combination (27–33)
- b) Proust
- b) Law of Conservation of Mass
- a) Two elements form more than one compound
- c) Law of Definite Proportions
- b) Law of Definite Proportions
- a) Simple fraction
- c) Dalton
Empirical & Molecular Formula (34–41)
- a) CH₂O
- b) 6
- c) C₃H₆O₃
- b) Ratio of atoms
- b) Molecular formula
- a) CH₂O
- a) Mass of each element per mole
- a) C₆H₆
Percentage Composition & Miscellaneous (42–50)
- a) 11%
- a) 58.5 g
- c) 1 mole of H₂O weighs 18 kg
- c) 2:16
- d) Both a & c
- b) 2
- a) Given 5 g H₂ reacts with 40 g O₂ to form water
- a) 98 g
- c) Stoichiometry deals with quantitative relationships in chemical reactions
Disclaimer:
All MCQs on this page are created for educational purposes. They are meant for practice and NEET/Class 11 Chemistry preparation only.