Here are 50 MCQs for Class 11 Chemistry Chapter 1 (Some Basic Concepts of Chemistry) based on NCERT syllabus, with answers and explanations:
1. Which of the following is a pure substance?
a) Milk
b) Sea water
c) 24-carat gold
d) Soil
Correct Answer: c
Explanation: 24-carat gold is elemental gold without impurities, making it a pure substance.
2. The SI unit of mass is:
a) Gram
b) Pound
c) Kilogram
d) Milligram
Correct Answer: c
Explanation: Kilogram (kg) is the SI base unit of mass.
3. Which law states that mass is conserved in a chemical reaction?
a) Law of definite proportions
b) Law of multiple proportions
c) Law of conservation of mass
d) Avogadro’s law
Correct Answer: c
Explanation: Law of conservation of mass (Lavoisier) states that mass remains constant in chemical reactions.
4. 1 mole of CO₂ contains:
a) 6.022 × 10²³ atoms
b) 6.022 × 10²³ molecules
c) 18.1 × 10²³ atoms
d) 3 g of carbon
Correct Answer: b
Explanation: 1 mole of any substance contains Avogadro’s number (6.022 × 10²³) of molecules.
5. The number of significant figures in 0.0025 is:
a) 1
b) 2
c) 3
d) 4
Correct Answer: b
Explanation: Leading zeros are not significant. Only “25” are significant digits.
6. Which of the following has the highest mass?
a) 1 g of Fe
b) 1 mole of S
c) 1 mole of O₂
d) 10²³ atoms of C
Correct Answer: b
Explanation:
- 1 mole of S = 32 g
- 1 mole of O₂ = 32 g
- 10²³ atoms of C = 10236.022×10236.022×10231023 moles ≈ 0.166 moles = 1.99 g
- 1 g of Fe = 1 g
Thus, 32 g (S or O₂) > others.
7. The molarity of 0.5 mol NaOH dissolved in 500 mL water is:
a) 0.5 M
b) 1.0 M
c) 2.0 M
d) 0.1 M
Correct Answer: b
Explanation: Molarity = molesvolume (L)=0.50.5=1.0volume (L)moles=0.50.5=1.0 M.
8. 2 g of H₂ reacts with 16 g of O₂ to give H₂O. The limiting reagent is:
a) H₂
b) O₂
c) H₂O
d) No limiting reagent
Correct Answer: a
Explanation:
- Reaction: 2H2+O2→2H2O2H2+O2→2H2O
- Moles of H₂ = 22=122=1 mol; requires 0.5 mol O₂.
- Moles of O₂ = 1632=0.53216=0.5 mol.
H₂ is limiting as 1 mol H₂ requires only 0.5 mol O₂, but here O₂ is sufficient.
9. The empirical formula of benzene (C₆H₆) is:
a) C₆H₆
b) CH
c) C₃H₃
d) C₂H₂
Correct Answer: b
Explanation: Simplest ratio C:H = 6:6 = 1:1 → CH.
10. The mass percentage of oxygen in CO₂ is:
a) 27.27%
b) 72.73%
c) 36.36%
d) 63.64%
Correct Answer: b
Explanation:
% O = 3244×100=72.73%4432×100=72.73%.
11. Which law explains that CO and CO₂ have different oxygen compositions?
a) Conservation of mass
b) Definite proportions
c) Multiple proportions
d) Gay-Lussac’s law
Correct Answer: c
Explanation: Law of multiple proportions: Elements combine in simple mass ratios when forming multiple compounds.
12. The number of moles in 11 g of CO₂ is:
a) 0.25
b) 0.5
c) 1.0
d) 2.0
Correct Answer: a
Explanation: Molar mass of CO₂ = 44 g/mol → Moles = 1144=0.254411=0.25.
13. 0.1 mol of CH₄ contains:
a) 6.022 × 10²² molecules
b) 3.0 × 10²³ atoms
c) 1.6 g of hydrogen
d) 2.4 g of carbon
Correct Answer: a
Explanation:
Molecules = 0.1 × 6.022 × 10²³ = 6.022 × 10²².
14. Density of water is 1 g/mL. The volume occupied by 1 molecule of water is:
a) 18 mL
b) 2.99 × 10⁻²³ mL
c) 1.08 × 10⁻²³ mL
d) 3.0 × 10⁻²² mL
Correct Answer: b
Explanation:
- Mass of 1 molecule = 186.022×10236.022×102318 g
- Volume = massdensity=186.022×1023×1≈2.99×10−23densitymass=6.022×1023×118≈2.99×10−23 mL.
15. The molality of a solution containing 18 g glucose in 500 g water is:
a) 0.1 m
b) 0.2 m
c) 0.5 m
d) 1.0 m
Correct Answer: b
Explanation:
Moles of glucose = 18180=0.118018=0.1 mol
Molality = 0.10.5=0.20.50.1=0.2 m.
16. Which has maximum atoms?
a) 1 g Au (atomic mass 197)
b) 1 g Na (atomic mass 23)
c) 1 g Li (atomic mass 7)
d) 1 g Cl₂ (molecular mass 71)
Correct Answer: c
Explanation:
Number of atoms ∝ Number of molesAtomic massAtomic massNumber of moles
Li has the smallest atomic mass → highest moles → highest atoms.
17. 1 a.m.u. is equal to:
a) 1 g
b) 112121 mass of C-12 atom
c) Mass of H atom
d) 1.66 × 10⁻²⁴ kg
Correct Answer: b
Explanation: 1 a.m.u. is defined as 112121th mass of a C-12 atom.
18. Which of the following is NOT a mixture?
a) Air
b) Brass
c) Distilled water
d) Gasoline
Correct Answer: c
Explanation: Distilled water is pure H₂O.
19. The number of significant figures in 100.0 is:
a) 1
b) 2
c) 3
d) 4
Correct Answer: d
Explanation: Trailing zeros after decimal are significant.
20. In 2 mol of ammonia (NH₃), total hydrogen atoms are:
a) 2 × 6.022 × 10²³
b) 3 × 6.022 × 10²³
c) 6 × 6.022 × 10²³
d) 4 × 6.022 × 10²³
Correct Answer: c
Explanation:
1 NH₃ has 3 H atoms → 2 mol NH₃ has 2 × 3 × 6.022 × 10²³ H atoms.
21. Which represents Avogadro’s number?
a) Atoms in 12 g of C-12
b) Molecules in 32 g O₂
c) Ions in 58.5 g NaCl
d) All of the above
Correct Answer: d
Explanation: All contain 1 mole of entities → 6.022 × 10²³.
22. The formula mass of Na₂CO₃·10H₂O is:
a) 106 u
b) 286 u
c) 180 u
d) 226 u
Correct Answer: b
Explanation:
2(23) + 12 + 3(16) + 10[2(1) + 16] = 46 + 12 + 48 + 180 = 286 u.
23. 0.5 molal NaOH solution means:
a) 0.5 mol NaOH in 1000 g solvent
b) 0.5 mol NaOH in 1000 mL solution
c) 0.5 g NaOH in 1000 g solvent
d) 20 g NaOH in 1000 g solvent
Correct Answer: a
Explanation: Molality = moles of solute per kg solvent.
24. 10 g CaCO₃ on heating gives CO₂:
a) 2.24 L at STP
b) 44 g
c) 4.4 g
d) 22.4 L
Correct Answer: c
Explanation:
CaCO3→CaO+CO2CaCO3→CaO+CO2
100 g CaCO₃ → 44 g CO₂ → 10 g CaCO₃ → 4.4 g CO₂.
25. The equivalent of 1 ppb is:
a) 1 part per 100
b) 1 part per 1000
c) 1 part per 10⁶
d) 1 part per 10⁹
Correct Answer: d
Explanation: ppb = parts per billion (10⁹).
26. Which is correct for 0.00052?
a) 5.2 × 10⁻⁴
b) 52 × 10⁻⁵
c) 0.52 × 10⁻³
d) Both a and c
Correct Answer: d
Explanation:
0.00052 = 5.2 × 10⁻⁴ = 0.52 × 10⁻³.
27. 10 mol of methane reacts with oxygen. Moles of CO₂ produced are:
a) 5
b) 10
c) 20
d) 40
Correct Answer: b
Explanation:
CH4+2O2→CO2+2H2OCH4+2O2→CO2+2H2O
1 mol CH₄ → 1 mol CO₂ → 10 mol CH₄ → 10 mol CO₂.
28. The molecular formula of glucose is C₆H₁₂O₆. Its empirical formula is:
a) C₆H₁₂O₆
b) CH₂O
c) C₂H₄O₂
d) CHO
Correct Answer: b
Explanation: Simplest ratio = 1:2:1 → CH₂O.
29. 1.0 × 10⁻² g of oxygen contains how many oxygen atoms?
a) 6.022 × 10²³
b) 3.76 × 10²⁰
c) 1.88 × 10²⁰
d) 1.88 × 10²³
Correct Answer: b
Explanation:
Moles of O = 1.0×10−216=6.25×10−4161.0×10−2=6.25×10−4
Atoms = 6.25 × 10⁻⁴ × 6.022 × 10²³ ≈ 3.76 × 10²⁰.
30. Which is NOT a unit of concentration?
a) Molality
b) Molarity
c) Density
d) Mole fraction
Correct Answer: c
Explanation: Density is mass/volume, not a concentration term.
31. The number of oxygen atoms in 4.4 g CO₂ is:
a) 1.2 × 10²³
b) 6.0 × 10²²
c) 6.0 × 10²³
d) 12.0 × 10²³
Correct Answer: a
Explanation:
Moles of CO₂ = 4.444=0.1444.4=0.1
O atoms = 0.1 × 2 × 6.022 × 10²³ = 1.2044 × 10²³ ≈ 1.2 × 10²³.
32. Gay-Lussac’s law deals with:
a) Mass conservation
b) Volume ratios of gases
c) Definite proportions
d) Multiple proportions
Correct Answer: b
Explanation: Gay-Lussac’s law states gases combine in simple volume ratios.
33. 100 mL of 0.1 M H₂SO₄ is mixed with 200 mL of 0.2 M NaOH. The mixture is:
a) Acidic
b) Basic
c) Neutral
d) None
Correct Answer: c
Explanation:
- H₂SO₄ moles = 0.1 × 0.1 = 0.01 → H⁺ = 0.02 mol
- NaOH moles = 0.2 × 0.2 = 0.04 mol OH⁻
- OH⁻ excess = 0.02 mol → Basic.
34. 4.4 g of an unknown gas occupies 2.24 L at STP. The gas is:
a) CO₂
b) N₂O
c) CO
d) O₂
Correct Answer: a
Explanation:
Molar mass = mass×22.4volume at STP=4.4×22.42.24=44volume at STPmass×22.4=2.244.4×22.4=44 g/mol → CO₂.
35. Precision refers to:
a) Closeness to true value
b) Reproducibility of measurements
c) Both a and b
d) None
Correct Answer: b
Explanation: Precision = reproducibility; Accuracy = closeness to true value.
36. The molar mass of H₃PO₄ is:
a) 98 u
b) 94 u
c) 96 u
d) 97 u
Correct Answer: a
Explanation: 3(1) + 31 + 4(16) = 3 + 31 + 64 = 98 u.
37. The mass of 1 molecule of oxygen is:
a) 16 g
b) 32 g
c) 326.022×10236.022×102332 g
d) 166.022×10236.022×102316 g
Correct Answer: c
Explanation: Mass of 1 O₂ molecule = 32NANA32 g.
38. 0.2 g of metal produces 0.281 g metal oxide. Equivalent mass of metal is:
a) 56
b) 28
c) 20
d) 40
Correct Answer: c
Explanation:
Mass of oxygen = 0.281 – 0.2 = 0.081 g
Equivalent mass = Mass of metalMass of oxygen×8=0.20.081×8≈20Mass of oxygenMass of metal×8=0.0810.2×8≈20.
39. Which pair follows law of multiple proportions?
a) H₂O, D₂O
b) NaCl, NaBr
c) CO, CO₂
d) NH₃, NCl₃
Correct Answer: c
Explanation: CO and CO₂ show mass ratio of O combining with fixed C as 16:32 = 1:2.
40. The percentage of nitrogen in NH₃ is:
a) 82.35%
b) 17.65%
c) 25%
d) 75%
Correct Answer: a
Explanation:
% N = 1417×100=82.35%1714×100=82.35%.
41. 500 mL of 0.2 M HCl diluted to 1 L. New molarity is:
a) 0.4 M
b) 0.2 M
c) 0.1 M
d) 0.05 M
Correct Answer: c
Explanation:
M₁V₁ = M₂V₂ → 0.2 × 0.5 = M₂ × 1 → M₂ = 0.1 M.
42. Which is a homogeneous mixture?
a) Salt solution
b) Sand and salt
c) Oil and water
d) Soil
Correct Answer: a
Explanation: Salt solution has uniform composition.
43. 0.1 mol of CaCO₃ contains:
a) 6.022 × 10²² Ca atoms
b) 3.0 × 10²³ O atoms
c) 6.022 × 10²² CO₃²⁻ ions
d) All of the above
Correct Answer: d
Explanation:
- Ca atoms = 0.1 × 6.022 × 10²³ = 6.022 × 10²²
- O atoms = 0.1 × 3 × 6.022 × 10²³ = 1.8066 × 10²³ ≈ 3 × 10²³? (Wait: 1.8 × 10²³ ≠ 3 × 10²³)
Correction: O atoms = 0.1 × 3 × 6.022 × 10²³ = 1.8066 × 10²³ (not 3 × 10²³).
Revised answer: a and c only.
*(Note: Option b is incorrect. O atoms = 1.8066 × 10²³, not 3.0 × 10²³)*
44. The scientific notation for 0.000043 is:
a) 4.3 × 10⁻⁵
b) 43 × 10⁻⁶
c) 4.3 × 10⁻⁴
d) 0.43 × 10⁻⁴
Correct Answer: a
Explanation: 0.000043 = 4.3 × 10⁻⁵.
45. 2 mol H₂ and 1 mol O₂ react to form H₂O. Moles of H₂O formed are:
a) 1
b) 2
c) 3
d) 4
Correct Answer: b
Explanation:
2H2+O2→2H2O2H2+O2→2H2O → 2 mol H₂ produce 2 mol H₂O.
46. Mass of 1 atom of C-12 is:
a) 12 g
b) 1.992 × 10⁻²³ g
c) 126.022×10236.022×102312 g
d) Both b and c
Correct Answer: d
Explanation:
Mass = 12NANA12 g = 1.992 × 10⁻²³ g.
47. The number of electrons in 1.8 mL H₂O (density = 1 g/mL) is:
a) 6.022 × 10²³
b) 3.011 × 10²³
c) 0.1001 × 10²³
d) None
Correct Answer: b
Explanation:
- Mass of H₂O = 1.8 g
- Moles = 1.818=0.1181.8=0.1
- Electrons in 1 H₂O = 10 (2H = 2e⁻, O=8e⁻)
- Total electrons = 0.1 × 10 × 6.022 × 10²³ = 6.022 × 10²³?
Correction:
0.1 mol × 10 mol electrons/mol × 6.022 × 10²³ electrons/mol = 6.022 × 10²³?
But: 0.1 mol molecules × (10 electrons/molecule) × N_A = 0.1 × 10 × N_A = N_A = 6.022 × 10²³.
Revised answer: a (6.022 × 10²³).
48. A compound contains 50% element X (atomic mass 10) and 50% Y (atomic mass 20). Empirical formula is:
a) XY
b) X₂Y
c) XY₂
d) X₂Y₃
Correct Answer: b
Explanation:
Mole ratio:
X = 5010=51050=5; Y = 5020=2.52050=2.5
Ratio = 5:2.5 = 2:1 → X₂Y.
49. 1.0 mol FeO contains Fe²⁺ ions:
a) 6.022 × 10²³
b) 12.044 × 10²³
c) 3.011 × 10²³
d) 1.0 g
Correct Answer: a
Explanation: 1 mol FeO → 1 mol Fe²⁺ → 6.022 × 10²³ ions.
50. The mass of 112 cm³ of CH₄ at STP is:
a) 0.16 g
b) 0.08 g
c) 0.8 g
d) 0.016 g
Correct Answer: b
Explanation:
22400 cm³ CH₄ at STP = 16 g
112 cm³ = 1622400×112=0.082240016×112=0.08 g.
Answer Key:
1.c, 2.c, 3.c, 4.b, 5.b, 6.b, 7.b, 8.a, 9.b, 10.b,
11.c, 12.a, 13.a, 14.b, 15.b, 16.c, 17.b, 18.c, 19.d, 20.c,
21.d, 22.b, 23.a, 24.c, 25.d, 26.d, 27.b, 28.b, 29.b, 30.c,
31.a, 32.b, 33.b, 34.a, 35.b, 36.a, 37.c, 38.c, 39.c, 40.a,
41.c, 42.a, 43.a, 44.a, 45.b, 46.d, 47.a, 48.b, 49.a, 50.b
(Note: Corrections applied to Q43 and Q47 as per explanations)