Chapter 2: Fundamental Concept of Atom and Molecules

1. Who proposed the Law of Conservation of Matter?

2.Who proposed the Law of Conservation of Mass?

3.In all samples of carbon monoxide, the mass ratio of carbon to oxygen is always 3:4. This confirms which law?

4.Which of the following options is not correctly matched?

Question: 6.3 g of NaHCO₃ reacts with 10 g of HCl solution to form NaCl and CO₂. If 12 g of NaCl is formed, what is the mass of CO₂ gas released in the reaction?
Answer: (c) 2.8 g ✅

Explanation:

The reaction is:

NaHCO₃+HCl→NaCl+H₂O+CO₂\text{NaHCO₃} + \text{HCl} → \text{NaCl} + \text{H₂O} + \text{CO₂}

• Mass of reactants = Mass of products (Law of Conservation of Mass)

Let mCO₂m_{\text{CO₂}} be the mass of CO₂:

Mass of NaHCO₃ + Mass of HCl=Mass of NaCl + Mass of CO₂ + Mass of H₂O\text{Mass of NaHCO₃ + Mass of HCl} = \text{Mass of NaCl + Mass of CO₂ + Mass of H₂O}

Assuming H₂O is not mentioned, the problem simplifies to:

6.3+10=12+mCO₂6.3 + 10 = 12 + m_{\text{CO₂}} mCO₂=16.3−12=4.3 g?m_{\text{CO₂}} = 16.3 - 12 = 4.3 \text{ g?}

Wait, the options don’t match exactly. Let’s calculate using stoichiometry instead:

Molar masses:

• NaHCO₃ = 84 g/mol
• NaCl = 58.5 g/mol
• CO₂ = 44 g/mol

From reaction: 1 mole NaHCO₃ → 1 mole NaCl + 1 mole CO₂

Mass ratio of NaCl to CO₂: 58.5 : 44

Let x = mass of CO₂ formed for 12 g NaCl:

58.544=12x  ⟹  x=12×4458.5≈9.02 g\frac{58.5}{44} = \frac{12}{x} \implies x = \frac{12 \times 44}{58.5} \approx 9.02 \text{ g}

Correct Answer: (d) 9.1 g ✅

So the mass of CO₂ released is approximately 9.1 g.

Do you want me to explain why my first shortcut method gave a wrong result?

6.Who first proposed the Atomic Theory?

7.According to Dalton’s Atomic Theory, which is the smallest particle that can exist independently?

8.Who proposed that the atom is indivisible?

9. According to Dalton’s Atomic Theory –

Which of the following is not correct?

11.Which concept of Dalton’s Atomic Theory can explain the Law of Conservation of Mass?

12.What is the smallest particle of an element that participates in a chemical reaction called?

13.Question: Consider the following statements:

All atoms of an element are identical, but they are different from the atoms of other elements.

Each atom of an element exhibits all the properties of that element.

Which of the above statements is/are true?

14.The average size of an atom is –

15.Which of the following elements has the smallest atom?

16.Consider the following statements:

1. John Dalton called the smallest particle of a compound a “compound molecule.”

2. Avogadro was the first to name the smallest particle of a compound as a “molecule.”

Which of the above statements is/are correct?

17.Phosphorus exists as –

18. Which of the following is monatomic?

19.Which of the following statements is false?

20. Which of the following information can be obtained from the chemical symbol of an element?

21. Consider the following statements:

1. The smallest particle of matter that does not exist freely and participates in chemical reactions is called an atom.
2. The smallest particle of matter that exists freely is called a molecule.

Which of the above statements is/are correct?

22.What is the atomicity of metallic elements?

23.Carbon is –

24.Consider the following statements –

1. Molecules are formed by the combination of two or more atoms of the same element.
2. Molecules cannot be formed by atoms of different elements.

Which of the above statements is/are correct?

25.Most atoms of elements are highly reactive; atoms are stable –

26.The number of atoms present in a molecule of a substance is called –

27.Which of the following exists as a monatomic molecule?

29. Which of the following is not a compound salt?

30. Which of the following is NOT a monovalent element?

32. Which of the following is an amphoteric ion?

31. The rule for oxidation number change during redox reaction is—

33. Which of the following elements forms variable valency compounds?

34. Consider the following statements:

1. Two or more chemically bonded atoms form an electrically neutral group called a molecule.
2. All atoms of an element are similar.
3. A molecule of a compound contains two or more atoms of different elements.

Which of the above statements is/are correct?

35. Formula of chromium sulphate is—

क्रोमियम सल्फेट का सूत्र होगा-

36. Formula of chloride of a bivalent metal is—

37. Formula of chloride of a metal M with oxide M₂O₃ is—

38. Formula of oxide of element Y with valency 4 is—

39. What is the term for combining of an element’s atoms with other atoms?

40. If the formula of aluminium compound with element X is Na₂X₃, then the empirical formula of aluminium compound with X will be—

41. Which of the following is a trivalent element?

42. Valency of A = 3 and valency of B = 2, then the formula of the compound will be—

43. If valency of A = 3 and valency of B = 6, formula will be—

44. If the atomic mass of element X is 16 times that of hydrogen, then its atomic mass will be—

45. The atomic mass of an element is the relative mass compared to 1/12th mass of—

46. Atomic mass unit (amu) is defined as—

47. 1 gram is equal to—

48. If magnesium’s atomic mass is 24 amu, then the mass in grams will be—

49. Consider the statements—

1. All atoms of an element have the same atomic mass.
2. Atoms of different elements may have the same atomic mass.

उपर्युक्त में कौन-सा से कथन सही है हैं ?

50. A 0.24 g sample of a compound of oxygen and bromine contains 0.096 g Br and 0.144 g O. What is the percentage of Br and O in the compound?

51. Which Dalton’s postulates are not completely correct?

52. When 3 g of carbon burns in 8 g of oxygen, 11 g of CO₂ are formed. If 3 g of carbon are burnt in 50 g of oxygen, how much CO₂ will form?

53. The molecular mass of calcium carbonate is—

54. Gram–molecular mass (molar mass) of water is—

55. Molecular mass of sulphuric acid (H₂SO₄) is—

56. By mass, H and O combine in the ratio 1:8 to form water. What mass of O₂ is needed to react completely with 3 g of H₂?

57. The Latin name of sodium is—

58. “Hydrargyrum” is the Latin name of—

59. On complete decomposition of 10 g CaCO₃, 5.6 g CaO is formed and the rest is CO₂. What mass of CO₂ is released?

62. Magnesium and oxygen combine by mass in the ratio 3:2 to form MgO. For complete reaction with 24 g Mg, how much O₂ is needed?

63. The composition (kinds and numbers of atoms) in a molecule is expressed by—

64.“If 100 grams of pure water taken from different sources is electrolyzed, it always yields 11 grams of hydrogen and 89 grams of oxygen.”

Which chemical law is illustrated by this statement?

65. Which ancient Indian philosopher suggested that matter is composed of extremely small particles?

66. The atomic mass of calcium is 40 amu. The number of moles in 5 g of calcium will be—

67. The mass of one mole of aluminium atoms will be how much? (Al = 27 amu)

68. The atomic mass of sodium is 23 amu. The number of moles in 5.75 g of sodium is—

69. The mass of a carbon atom is 12 amu. The mass of one carbon atom in grams will be—

70. Which of the following is the correct mole-to-mass relationship?

71. The number of molecules in a 2.8 g sample of nitrogen gas will be—

72. If 12 g of carbon contains Avogadro’s number of atoms, the number of atoms in 1 g of carbon will be

73. The number of moles in 12.046×10 ke power 23 oxygen atoms will be—

74. The number of atoms in 0.5 mole of hydrogen is—

75. In one mole of CO₂, there are—

76. The mass of 0.7 mole of O₂ gas is—

77. The number of moles in 85 g of Cr₂S₃ is—

78. The element M has an atomic mass of 2.65 × 10⁻³ g per atom. M is—

79. If the number of atoms in X grams of calcium is equal to the number of atoms in 4 g of helium, the value of X will be—

80. The number of moles in 22 g of carbon dioxide is—

81. The mass of 0.5 mole of water (H₂O) is—

83. A person buys 10 moles of water from a shop, with each bottle containing 20 g. How many bottles will the person receive?

82. The number of atoms in 0.051 mole of aluminium oxide (Al₂O₃) is—

84. The mass of 5 moles of ammonia (NH₃) will be—

85. What will be the mass of 5 moles of sodium carbonate (Na₂CO₃)?

86. How many water molecules are there in a drop of water weighing 0.06 g?

87. What will be the volume of 14 g of nitrogen (N₂) gas at NTP?

88. The number of molecules present in 16 g of oxygen is equal to the number of molecules in which of the following?

89. What will be the volume of 8 g of oxygen at NTP?

90. Which of the following will have the highest volume at NTP?

91. How many moles are there in 12.044×10 ke power 23 molecules of sulfur dioxide (SO₂)?

92. What will be the mass of 3.011×10 ke power 24 molecules of nitrogen gas (N₂)?

93. How many moles are there in 160 g of sodium hydroxide (NaOH)?

94. If the atomic mass of zinc is 65.41 amu, what will be the mass in grams of 2.42 moles of zinc?

95. What will be the volume in liters of 20 g of hydrogen gas (H₂) at standard temperature and pressure (STP)?

96. How many moles of sulfur are there in 294 g of H₂SO₄?

97. What is the mass of oxygen present in 1 kg of potassium nitrate (KNO₃)?

98.    1 mole of CaCO₃ contains what percentage of calcium (Ca)?

99. In 1 mole of H₂SO₄, what is the percentage of sulfur (S)?

100. What is the value of Avogadro’s constant?