Atoms and Molecules Class 9 MCQ

Atoms: Atoms are the basic building blocks of matter. They are the smallest units of an element that retain its properties. Atoms are made up of subatomic particles: protons, neutrons, and electrons.

Molecules: Molecules are formed when two or more atoms chemically combine. They can be composed of atoms of the same element (e.g., O2) or different elements (e.g., H2O).

Importance: Understanding atoms and molecules is fundamental to understanding the composition and behavior of matter, which is essential in various scientific fields and everyday life.

Atoms 

Structure of an Atom: An atom consists of a nucleus at its center, which contains protons (positively charged particles) and neutrons (neutral particles). Electrons, negatively charged particles, orbit the nucleus in specific energy levels called orbitals or electron shells.

Subatomic Particles: The three main subatomic particles in an atom are protons, neutrons, and electrons, each with specific properties like mass and charge.

Atomic Number and Mass Number: The atomic number is the number of protons in an atom, which uniquely identifies an element. The mass number is the sum of protons and neutrons in an atom.

Atomic Symbol and Notation: Each element is represented by its atomic symbol (e.g., H for hydrogen, O for oxygen). The notation represents the atomic mass, atomic number, and symbol of an element (e.g., ¹²C for carbon-12).

Atomic Models: Various scientists proposed models to understand the structure of an atom, including Dalton's, Thomson's, Rutherford's, Bohr's, and the Quantum Mechanical Model.

Molecules

Definition and Formation: Molecules are formed when atoms of different elements or the same element chemically bond together. They can be composed of a fixed number of atoms (e.g., H2O) or form a large and complex structure (e.g., proteins).

Types of Molecules: Molecules can be classified as diatomic (composed of two atoms, like O2) or polyatomic (composed of more than two atoms, like H2O).

Molecular Formulas: Molecular formulas indicate the number and types of atoms present in a molecule (e.g., CO2 for carbon dioxide).

Chemical Bonds: Chemical bonds are forces that hold atoms together in a molecule. The main types are ionic bonds (transfer of electrons), covalent bonds (sharing of electrons), and metallic bonds (electrons delocalized throughout a metal lattice).

Chemical Reactions

Reactants and Products: Chemical reactions involve the transformation of reactants into products through the breaking and forming of chemical bonds.

Conservation of Mass: In a chemical reaction, the total mass of the reactants equals the total mass of the products.

Types of Chemical Reactions: Different types include synthesis/combination, decomposition, single replacement, double replacement, and combustion.

Properties of Atoms and Molecules

Atomic Size and Radius: The size of an atom is determined by the electron cloud's outer boundary, often referred to as the atomic radius.

Ionization Energy: The energy required to remove an electron from an atom, forming an ion.

Electronegativity: The tendency of an atom to attract shared electrons in a covalent bond.

Molecular Shape and Polarity: The arrangement of atoms in a molecule and whether the molecule is polar or non-polar.

Periodic Table

Organization of Elements: Elements are arranged in order of increasing atomic number in rows (periods) and columns (groups) on the periodic table.

Periods and Groups: Elements in the same period have the same number of electron shells, while elements in the same group have similar chemical properties due to similar valence electron configurations.

States of Matter

Solid, Liquid, Gas: The three fundamental states of matter determined by the arrangement and motion of particles.

Changes of State: Transitions between states due to the addition or removal of energy.

Applications

Importance of Atoms and Molecules in Daily Life: Understanding atoms and molecules is crucial in fields like medicine, industry, environmental science, and technology.

Use of Molecules in Various Industries: Molecules are utilized in creating materials, medicines, and various products.

101 multiple-choice questions (MCQs) on atoms and molecules for Class 9, along with their answers and explanations:

1. Q: What is the smallest unit of an element that retains its chemical properties?

   a) Atom

   b) Molecule

   c) Ion

   d) Compound

   Answer: a) Atom

   Explanation: An atom is the smallest unit of an element that retains its unique

chemical properties.

2. Q: The number of protons in the nucleus of an atom is called its:

   a) Atomic mass

   b) Atomic number

   c) Mass number

   d) Electronegativity

   Answer: b) Atomic number

   Explanation: The atomic number of an element is equal to the number of protons

in the nucleus of its atom.

3. Q: The mass number of an atom is equal to the sum of:

   a) Protons and neutrons

   b) Protons and electrons

   c) Electrons and neutrons

   d) Protons, electrons, and neutrons

   Answer: a) Protons and neutrons

   Explanation: The mass number is the total number of protons and neutrons in

the atom's nucleus.

4. Q: Isotopes of an element have the same number of:

   a) Protons

   b) Electrons

   c) Neutrons

   d) All of the above

   Answer: a) Protons

   Explanation: Isotopes have the same number of protons but different

numbers of neutrons.

5. Q: Which subatomic particle is responsible for determining the chemical properties

of an element?

   a) Protons

   b) Neutrons

   c) Electrons

   d) Nucleus

   Answer: c) Electrons

   Explanation: The arrangement and number of electrons in an atom are responsible

for its chemical properties.

6. Q: The symbol of an element represents its:

   a) Number of protons

   b) Atomic mass

   c) Atomic number

   d) Number of neutrons

   Answer: c) Atomic number

   Explanation: The symbol of an element represents its atomic number.

7. Q: What is the charge of a proton?

   a) Positive

   b) Negative

   c) Neutral

   d) None of the above

   Answer: a) Positive

   Explanation: Protons carry a positive charge.

8. Q: The mass of an electron is approximately equal to the mass of:

   a) A proton

   b) A neutron

   c) An alpha particle

   d) Negligible compared to protons and neutrons

   Answer: d) Negligible compared to protons and neutrons

   Explanation: The mass of an electron is much smaller than that of a proton or neutron.

9. Q: The sum of the number of protons and neutrons in an atom gives its:

   a) Atomic number

   b) Atomic mass

   c) Isotopic number

   d) Mass number

   Answer: d) Mass number

   Explanation: The mass number of an atom is the sum of its protons and neutrons.

10. Q: The electronic configuration of chlorine (Cl) is 2, 8, 7. How many valence electrons does chlorine have?

    a) 2

    b) 7

    c) 8

    d) 17

    Answer: b) 7

    Explanation: The outermost shell of chlorine contains 7 electrons,

which are valence electrons.

11. Q: A molecule is formed when:

    a) Two or more different elements chemically combine.

    b) Two or more atoms of the same element chemically combine.

    c) Two or more isotopes combine.

    d) Two or more ions combine.

    Answer: a) Two or more different elements chemically combine.

    Explanation: A molecule is formed when atoms of different elements combine

through chemical bonding.

atoms and molecules class 9 mcq online test

12. Q: Which of the following is an example of a compound?

    a) Hydrogen gas (H2)

    b) Oxygen gas (O2)

    c) Carbon monoxide (CO)

    d) Helium gas (He)

    Answer: c) Carbon monoxide (CO)

    Explanation: Carbon monoxide (CO) is a compound composed of carbon and

oxygen atoms.

13. Q: The chemical formula H2O represents:

    a) Hydrogen gas

    b) Oxygen gas

    c) Water

    d) Hydrogen peroxide

    Answer: c) Water

    Explanation: H2O is the chemical formula for water.

14. Q: The chemical formula for carbon dioxide is:

    a) CO

    b) CO2

    c) C2O

    d) C2O2

    Answer: b) CO2

    Explanation: Carbon dioxide is represented by the chemical formula CO2.

15. Q: How many atoms are present in a single molecule of water (H2O)?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: b) 2

    Explanation: A water molecule (H2O) consists of two hydrogen atoms and

one oxygen atom.

16. Q: The molecular formula of methane is:

    a) CH4

    b) C2H6

    c) CO2

    d) H2O

    Answer: a) CH4

    Explanation: Methane is represented by the chemical formula CH4.

17. Q: How many hydrogen atoms are present in a methane (CH4) molecule?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: d) 4

    Explanation: Methane (CH4) contains four hydrogen atoms.

18. Q: Which of the following is a noble gas?

    a) Oxygen (O)

    b) Nitrogen (N)

    c) Helium (He)

    d) Hydrogen (H)

    Answer: c) Helium (He)

    Explanation: Helium is a noble gas, found in Group 18 of the periodic table.

19. Q: The chemical formula NaCl represents:

    a) Sodium chloride

    b) Nitric acid

    c) Sulfuric acid

    d) Sodium carbonate

    Answer: a) Sodium chloride

    Explanation: NaCl is the chemical formula for sodium chloride,

commonly known as table salt.

20. Q: How many atoms are present in one molecule of sodium chloride (NaCl)?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: b) 2

    Explanation: Sodium chloride (NaCl) is composed of one sodium atom and

one chlorine atom.

21. Q: The formula of sulfuric acid is:

    a) H2SO4

    b) H2SO3

    c) H2S

    d) H2O

    Answer: a) H2SO4

    Explanation: Sulfuric acid is represented by the chemical formula H2SO4.

22. Q: Which of the following is a diatomic molecule?

    a) O2

    b) CO2

    c) CH4

    d) H2O

    Answer: a) O2

    Explanation: Oxygen gas (O2) exists as diatomic molecules.

atoms and molecules class 9 mcq with answers pdf

23. Q: The molecular formula of ammonia is:

    a) NH3

    b) N2H4

    c) N2H2

    d) NH4

    Answer: a) NH3

    Explanation: Ammonia is represented by the chemical formula NH3.

24. Q: How many hydrogen atoms are present in an ammonia (NH3) molecule?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: c) 3

    Explanation: Ammonia (NH3) contains three hydrogen atoms.

25. Q: The formula of carbonic acid is:

    a) H2CO3

    b) HCO3

    c) CH4O3

    d) CO2H

    Answer: a) H2CO3

    Explanation: Carbonic acid is represented by the chemical formula H2CO3.

26. Q: The molecular formula of ethane is:

    a) C2H4

    b) C2H6

    c) C3H8

    d) C4H10

    Answer: b) C2H6

    Explanation: Ethane is represented by the chemical formula C2H6.

27. Q: How many carbon atoms are present in an ethane (C2H6) molecule?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: b) 2

    Explanation: Ethane (C2H6) contains two carbon atoms.

28. Q: The molecular formula of butane is:

    a) C2H4

    b) C2H6

    c) C3H8

    d) C4H10

    Answer: d) C4H10

    Explanation: Butane is represented by the chemical formula C4H10.

29. Q: How many hydrogen atoms are present in a butane (C4H10) molecule?

    a) 4

    b) 6

    c) 8

    d) 10

    Answer: d) 10

    Explanation: Butane (C4H10) contains ten hydrogen atoms.

30. Q: The molecular formula of ethanol is:

    a) C2H4O

    b) C2H6O

    c) C3H8O

    d) C2H5OH

    Answer: d) C2H5OH

    Explanation: Ethanol is represented by the chemical formula C2H5OH.

31. Q: How many oxygen atoms are present in one molecule of ethanol (C2H5OH)?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: a) 1

    Explanation: Ethanol (C2H5OH) contains one oxygen atom.

32. Q: Which of the following is an example of a heterogeneous mixture?

    a) Saltwater

    b) Air

    c) Oil and water

    d) Brass

    Answer: c) Oil and water

    Explanation: Oil and water form a heterogeneous mixture because

they do not mix evenly.

33. Q: Which of the following is an example of a homogeneous mixture?

    a) Soil

    b) Concrete

    c) Sugar dissolved in water

    d) Granite

    Answer: c) Sugar dissolved in water

    Explanation: When sugar dissolves in water, it forms a homogeneous mixture

as it is uniformly distributed.

34. Q: Which of the following statements about a mixture is correct?

    a) The properties of a mixture are constant throughout.

    b) A mixture always contains two or more elements.

    c) The composition of a mixture cannot be separated by physical means.

    d) A mixture is always in a fixed proportion.

    Answer: a) The properties of a mixture are constant throughout.

    Explanation: In a mixture, the properties can vary at different points,

and the composition is not fixed.

35. Q: Which of the following is an example of a compound?

    a) Air

    b) Water

    c) Saltwater

    d) Soil

    Answer: b) Water

    Explanation: Water (H2O) is a compound composed of hydrogen and oxygen.

36. Q: Which of the following is not a characteristic of a compound?

    a) The elements in a compound are chemically bonded.

    b) The composition of a compound can vary.

    c) The properties of a compound are different from its constituent elements.

    d) The elements in a compound can be separated by physical means.

    Answer: d) The elements in a compound can be separated by physical means.

    Explanation: Compounds are formed by chemical bonding, and their

elements cannot be separated by physical means.

37. Q: What is the total number of oxygen atoms in two molecules of carbon dioxide (CO2)?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: d) 4

    Explanation: Two molecules of carbon dioxide (CO2) contain four oxygen atoms.

38. Q: Which of the following elements is a metal?

    a) Chlorine (Cl)

    b) Oxygen (O)

    c) Sodium (Na)

    d) Sulfur (S)

    Answer: c) Sodium (Na)

    Explanation: Sodium is a metal, found in Group 1 of the periodic table.

39. Q: Which of the following elements is a non-metal?

    a) Calcium (Ca)

    b) Nitrogen (N)

    c) Potassium (K)

    d) Magnesium (Mg)

    Answer: b) Nitrogen (N)

    Explanation: Nitrogen is a non-metal, found in Group 15 of the periodic table.

40. Q: Which of the following elements is a metalloid?

    a) Silicon (Si)

    b) Iron (Fe)

    c) Gold (Au)

    d) Carbon (C)

    Answer: a) Silicon (Si)

    Explanation: Silicon is a metalloid, found between metals and non-metals on

the periodic table.

41. Q: The atomic number of an element is determined by the number of:

    a) Protons

    b) Neutrons

    c) Electrons

    d) Nucleons

    Answer: a) Protons

    Explanation: The atomic number of an element is equal to the number

of protons in its nucleus.

42. Q: The mass number of an element is determined by the number of:

    a) Protons

    b) Neutrons

    c) Electrons

    d) Nucleons

    Answer: d) Nucleons

    Explanation: The mass number represents the total number of protons and neutrons

in an atom.

43. Q: The number of protons in the nucleus of an atom is equal to the number

 of:

    a) Electrons

    b) Neutrons

    c) Valence electrons

    d) Isotopes

    Answer: a) Electrons

    Explanation: The number of protons in an atom is equal to the number of

electrons in its neutral state.

44. Q: What is the total number of nucleons (protons and neutrons) in an atom

with atomic number 20 and mass number 40?

    a) 20

    b) 40

    c) 60

    d) 80

    Answer: b) 40

    Explanation: The total number of nucleons in this atom is the mass number (40).

45. Q: Which of the following particles has a positive charge?

    a) Electron

    b) Neutron

    c) Proton

    d) Alpha particle

    Answer: c) Proton

    Explanation: Protons carry a positive charge.

46. Q: Which of the following particles has no charge?

    a) Electron

    b) Neutron

    c) Proton

    d) Alpha particle

    Answer: b) Neutron

    Explanation: Neutrons have no charge; they are neutral particles.

47. Q: The atomic number of an atom with 19 protons is:

    a) 1

    b) 19

    c) 38

    d) 57

    Answer: b) 19

    Explanation: The atomic number is the number of protons, which is 19 in this case.

48. Q: What is the atomic number of an atom that contains 26 electrons and 30 neutrons?

    a) 26

    b) 30

    c) 56

    d) 56.5

    Answer: a) 26

    Explanation: The atomic number is equal to the number of protons, which is also 26.

49. Q: The atomic mass of an element is determined by the number of:

    a) Protons

    b) Neutrons

    c) Electrons

    d) Valence electrons

    Answer: b) Neutrons

    Explanation: The atomic mass is influenced by the total number of protons and neutrons.

50. Q: What is the atomic mass of an element that contains 20 protons and 20 neutrons?

    a) 20

    b) 40

    c) 60

    d) 80

    Answer: b) 40

    Explanation: The atomic mass is the total number of protons and neutrons,

which is 40 in this case.

51. Q: How many protons are present in an atom with atomic number 17?

    a) 7

    b) 17

    c) 27

    d) 35

    Answer: b) 17

    Explanation: The atomic number (17) represents the number of protons.

52. Q: The nucleus of an atom contains:

    a) Electrons and protons

    b) Protons and neutrons

    c) Neutrons and electrons

    d) Protons, neutrons, and electrons

    Answer: b) Protons and neutrons

    Explanation: The nucleus contains protons and neutrons, while electrons

are found in electron shells.

53. Q: Electrons are distributed around the nucleus of an atom in:

    a) Electron shells or energy levels

    b) Nucleus

    c) Proton rings

    d) Electron clouds

    Answer: a) Electron shells or energy levels

    Explanation: Electrons occupy specific energy levels or shells around the nucleus.

54. Q: How many electrons can the first energy level (K shell) hold?

    a) 2

    b) 4

    c) 8

    d) 10

    Answer: a) 2

    Explanation: The first energy level can hold a maximum of 2 electrons.

55. Q: How many electrons can the second energy level (L shell) hold?

    a) 2

    b) 4

    c) 8

    d) 10

    Answer: c) 8

    Explanation: The second energy level can hold a maximum of 8 electrons.

56. Q: The electron configuration of an atom with 8 electrons is:

    a) 2, 6

    b) 2, 8

    c) 2, 8, 2

    d) 2, 8, 8

    Answer: b) 2, 8

    Explanation: The electron configuration of an atom with 8 electrons is

2 in the first shell and 8 in the second shell.

57. Q: How many valence electrons are present in an atom with electron

configuration 2, 8, 7?

    a) 2

    b) 7

    c) 8

    d) 17

    Answer: b) 7

    Explanation: The outermost shell contains 7 electrons, which are valence electrons.

atoms and molecules class 9 mcq with answers

58. Q: How many valence electrons are present in an atom with electron

configuration 2, 8, 5?

    a) 2

    b) 5

    c) 8

    d) 15

    Answer: b) 5

    Explanation: The outermost shell contains 5 electrons, which are valence electrons.

59. Q: Which of the following elements has the electron configuration 2, 8, 8, 2?

    a) Oxygen (O)

    b) Neon (Ne)

    c) Calcium (Ca)

    d) Magnesium (Mg)

    Answer: d) Magnesium (Mg)

    Explanation: Magnesium has the electron configuration 2, 8, 8, 2.

60. Q: Which of the following elements has the electron configuration 2, 8, 8?

    a) Nitrogen (N)

    b) Neon (Ne)

    c) Carbon (C)

    d) Oxygen (O)

    Answer: b) Neon (Ne)

    Explanation: Neon has the electron configuration 2, 8, 8.

61. Q: When an atom gains one or more electrons, it becomes a/an:

    a) Cation

    b) Anion

    c) Isotope

    d) Ion

    Answer: b) Anion

    Explanation: An atom that gains electrons becomes negatively charged

and is called an anion.

62. Q: When an atom loses one or more electrons, it becomes a/an:

    a) Cation

    b) Anion

    c) Isotope

    d) Ion

    Answer: a) Cation

    Explanation: An atom that loses electrons becomes positively charged

and is called a cation.

63. Q: The charge of an ion is determined by the number of:

    a) Protons

    b) Neutrons

    c) Electrons

    d) Nucleons

    Answer: c) Electrons

    Explanation: The charge of an ion is determined by the number of

electrons gained or lost.

64. Q: A cation is formed when an

 atom:

    a) Gains electrons

    b) Loses electrons

    c) Gains protons

    d) Loses protons

    Answer: b) Loses electrons

    Explanation: A cation is formed when an atom loses electrons, resulting

in a positive charge.

65. Q: Which of the following ions has a positive charge?

    a) Cl-

    b) Na+

    c) O2-

    d) F-

    Answer: b) Na+

    Explanation: Na+ is a cation and has a positive charge due to the loss of one electron.

66. Q: Which of the following ions has a negative charge?

    a) Cl-

    b) Na+

    c) O2-

    d) F-

    Answer: c) O2-

    Explanation: O2- is an anion and has a negative charge due to the gain

of two electrons.

67. Q: Which of the following ions has a 2+ charge?

    a) Ca2+

    b) Mg2-

    c) K+

    d) Br-

    Answer: a) Ca2+

    Explanation: Ca2+ has a 2+ charge due to the loss of two electrons.

68. Q: Which of the following ions has a 2- charge?

    a) Ca2+

    b) Mg2-

    c) K+

    d) Br-

    Answer: b) Mg2-

    Explanation: Mg2- has a 2- charge due to the gain of two electrons.

69. Q: The chemical formula for sodium chloride is:

    a) Na2Cl

    b) NaCl2

    c) NaCl

    d) Na2Cl2

    Answer: c) NaCl

    Explanation: Sodium chloride is represented by the chemical formula NaCl.

70. Q: What is the formula for calcium carbonate?

    a) Ca(CO3)2

    b) CaCO3

    c) Ca2CO3

    d) Ca2(CO3)3

    Answer: b) CaCO3

    Explanation: Calcium carbonate is represented by the chemical formula CaCO3.

71. Q: The chemical formula for sulfuric acid is:

    a) H2SO4

    b) HSO4

    c) H2SO3

    d) HSO3

    Answer: a) H2SO4

    Explanation: Sulfuric acid is represented by the chemical formula H2SO4.

72. Q: What is the formula for carbonic acid?

    a) H2CO4

    b) HCO3

    c) H2CO3

    d) HCO3-

    Answer: c) H2CO3

    Explanation: Carbonic acid is represented by the chemical formula H2CO3.

73. Q: The chemical formula for hydrogen peroxide is:

    a) H2O2

    b) H2O

    c) H2O4

    d) H2O3

    Answer: a) H2O2

    Explanation: Hydrogen peroxide is represented by the chemical formula H2O2.

74. Q: The chemical formula for glucose is:

    a) C12H6O6

    b) C6H12O6

    c) C6H6O6

    d) C12H12O6

    Answer: b) C6H12O6

    Explanation: Glucose is represented by the chemical formula C6H12O6.

75. Q: What is the chemical formula for acetic acid?

    a) C2H4O2

    b) C2H2O2

    c) CH3COOH

    d) CH3COO-

    Answer: c) CH3COOH

    Explanation: Acetic acid is represented by the chemical formula CH3COOH.

76. Q: Which of the following is a compound?

    a) Helium (He)

    b) Nitrogen (N2)

    c) Water (H2O)

    d) Neon (Ne)

    Answer: c) Water (H2O)

    Explanation: Water (H2O) is a compound.

77. Q: Which of the following is a molecule?

    a) Hydrogen (H)

    b) Sodium (Na)

    c) Oxygen (O2)

    d) Chlorine (Cl-)

    Answer: c) Oxygen (O2)

    Explanation: Oxygen (O2) is a molecule consisting of two oxygen atoms.

78. Q: The molecular formula for methane is:

    a) CH3

    b) CH4

    c) C2H4

    d) C2H6

    Answer: b) CH4

    Explanation: Methane is represented by the chemical formula CH4.

79. Q: The molecular formula for carbon dioxide is:

    a) CO

    b) CO2

    c) C2O

    d) C2O2

    Answer: b) CO2

    Explanation: Carbon dioxide is represented by the chemical formula CO2.

80. Q: Which of the following is a molecular compound?

    a) NaCl

    b) CO2

    c) CaCl2

    d) KBr

    Answer: b) CO2

    Explanation: CO2 is a molecular compound composed of two non-metal elements.

atoms and molecules class 9 mcq test

81. Q: Which of the following is an example of a network solid?

    a) Sodium chloride (NaCl)

    b) Diamond (C)

    c) Carbon dioxide (CO2)

    d) Oxygen gas (O2)

    Answer: b) Diamond (C)

    Explanation: Diamond is a network solid, with carbon atoms bonded in a

repeating pattern.

82. Q: Which of the following is an example of a molecular element?

    a) Oxygen (O2)

    b) Sodium (Na)

    c) Aluminum (Al)

    d) Fluorine (F2)

    Answer: a) Oxygen (O2)

    Explanation: Oxygen exists as O2 molecules, making it a molecular element.

83. Q: What is the molecular formula for sulfur dioxide?

    a) SO

    b) SO2

    c) S2O

    d) S2O2

    Answer: b) SO2

    Explanation: Sulfur dioxide is represented by the chemical formula SO2.

84. Q: The molecular formula for water is:

    a) H2O

    b) H2O2

    c) H2O3

    d) H3O

    Answer: a) H2O

    Explanation: Water is represented by the chemical formula H2O.

85. Q: Which of the following is an example of an ionic compound?

    a) Carbon dioxide (CO2)

    b) Sodium chloride (NaCl)

    c) Hydrogen peroxide (H2O2)

    d) Methane (CH4)

    Answer: b) Sodium chloride (NaCl)

    Explanation: Sodium chloride (NaCl) is an ionic compound composed of

sodium and chlorine ions.

86. Q: How many oxygen atoms are present in one molecule of sulfuric acid

 (H2SO4)?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: d) 4

    Explanation: Sulfuric acid (H2SO4) contains four oxygen atoms.

87. Q: How many oxygen atoms are present in one molecule of carbon dioxide (CO2)?

    a) 1

    b) 2

    c) 3

    d) 4

    Answer: b) 2

    Explanation: Carbon dioxide (CO2) contains two oxygen atoms.

88. Q: Which of the following is an example of a polar molecule?

    a) Oxygen (O2)

    b) Nitrogen (N2)

    c) Carbon dioxide (CO2)

    d) Water (H2O)

    Answer: d) Water (H2O)

    Explanation: Water (H2O) is a polar molecule due to its uneven distribution of charge.

89. Q: Which of the following is an example of a nonpolar molecule?

    a) Oxygen (O2)

    b) Hydrogen fluoride (HF)

    c) Carbon dioxide (CO2)

    d) Ammonia (NH3)

    Answer: a) Oxygen (O2)

    Explanation: Oxygen (O2) is a nonpolar molecule.

90. Q: How many total atoms are there in one molecule of calcium carbonate (CaCO3)?

    a) 5

    b) 6

    c) 7

    d) 8

    Answer: b) 6

    Explanation: Calcium carbonate (CaCO3) contains 3 oxygen atoms, 1 carbon atom,

and 1 calcium atom.

91. Q: The chemical formula for hydrochloric acid is:

    a) HCl

    b) HCl2

    c) H2Cl

    d) H2Cl2

    Answer: a) HCl

    Explanation: Hydrochloric acid is represented by the chemical formula HCl.

92. Q: What is the chemical formula for ammonia gas?

    a) NH4

    b) NH3

    c) N2H4

    d) N2H2

    Answer: b) NH3

    Explanation: Ammonia gas is represented by the chemical formula NH3.

93. Q: Which of the following elements is a halogen?

    a) Hydrogen (H)

    b) Oxygen (O)

    c) Chlorine (Cl)

    d) Calcium (Ca)

    Answer: c) Chlorine (Cl)

    Explanation: Chlorine is a halogen, found in Group 17 of the periodic table.

94. Q: Which of the following elements is an alkali metal?

    a) Helium (He)

    b) Neon (Ne)

    c) Sodium (Na)

    d) Potassium (K)

    Answer: c) Sodium (Na)

    Explanation: Sodium is an alkali metal, found in Group 1 of the periodic table.

95. Q: Which of the following elements is an alkaline earth metal?

    a) Lithium (Li)

    b) Beryllium (Be)

    c) Carbon (C)

    d) Nitrogen (N)

    Answer: b) Beryllium (Be)

    Explanation: Beryllium is an alkaline earth metal, found in Group 2 of the periodic table.

96. Q: Which of the following elements is a noble gas?

    a) Helium (He)

    b) Neon (Ne)

    c) Nitrogen (N)

    d) Oxygen (O)

    Answer: b) Neon (Ne)

    Explanation: Neon is a noble gas, found in Group 18 of the periodic table.

97. Q: Which of the following elements is a transition metal?

    a) Iron (Fe)

    b) Aluminum (Al)

    c) Silicon (Si)

    d) Copper (Cu)

    Answer: a) Iron (Fe)

    Explanation: Iron is a transition metal, found in the middle of the periodic table.

atoms and molecules class 9 mcq pdf

98. Q: Which of the following elements is a lanthanide?

    a) Uranium (U)

    b) Mercury (Hg)

    c) Europium (Eu)

    d) Silver (Ag)

    Answer: c) Europium (Eu)

    Explanation: Europium is a lanthanide element, found in the f-block of the periodic table.

99. Q: Which of the following elements is an actinide?

    a) Thorium (Th)

    b) Platinum (Pt)

    c) Iodine (I)

    d) Chromium (Cr)

    Answer: a) Thorium (Th)

    Explanation: Thorium is an actinide element, found in the f-block of the periodic table.

100. Q: What is the symbol for the element with atomic number 7?

    a) N

    b) C

    c) O

    d) Ne

    Answer: a) N

    Explanation: The symbol for the element with atomic number 7 is N, which

stands for nitrogen.

101. Q: What is the symbol for the element with atomic number 26?

    a) N

    b) C

    c) O

    d) Fe

    Answer: d) Fe

    Explanation: The symbol for the element with atomic number 26 is Fe, which

tands for iron.