Chapter 2 - "Atoms, Elements and Compound" - MCQ's

"Atoms, Elements and Compound" - MCQ's:-

1) Which statement best describes an element?
A. Two or more substances chemically combined
B. A pure substance made of only one type of atom
C. A substance made of ions in a lattice
D. A mixture of molecules
Answer: B
Reason: An element contains only one type of atom.

2) Which is a compound?
A. Oxygen gas
B. Iron
C. Water
D. Air
Answer: C
Reason: Water contains hydrogen and oxygen chemically bonded in a fixed ratio.

3) Which is a mixture?
A. Sodium chloride
B. Carbon dioxide
C. Air
D. Magnesium oxide
Answer: C
Reason: Air is a physical mix of gases.

4) A compound can be separated into its elements by:
A. Filtration
B. Distillation
C. Evaporation
D. Chemical reactions
Answer: D
Reason: Compounds require chemical changes to break bonds.

5) A mixture can be separated by:
A. Only chemical methods
B. Physical methods
C. Breaking covalent bonds
D. Nuclear reactions
Answer: B
Reason: Mixtures are not chemically combined.

6) The nucleus of an atom contains:
A. Electrons and neutrons
B. Protons and electrons
C. Protons and neutrons
D. Neutrons only
Answer: C
Reason: Protons and neutrons are in the nucleus.

7) Which particle has a charge of −1?
A. Proton
B. Neutron
C. Electron
D. Nucleon
Answer: C
Reason: Electrons are negatively charged.

8) Which particle has relative mass 1?
A. Electron
B. Proton
C. Electron and proton
D. Electron and neutron
Answer: B
Reason: Proton has relative mass 1 (neutron also 1, but only proton is listed alone).

9) The relative mass of an electron is:
A. 1
B. 1/2
C. 1/1836
D. 1836
Answer: C
Reason: Electron is much lighter than proton/neutron.

10) The atomic number (proton number) is the number of:
A. Neutrons only
B. Protons only
C. Protons + neutrons
D. Electrons + neutrons
Answer: B
Reason: Atomic number = number of protons.

11) The mass number (nucleon number) is the total number of:
A. Protons + electrons
B. Neutrons + electrons
C. Protons + neutrons
D. Protons only
Answer: C
Reason: Mass number counts nucleons (protons and neutrons).

12) An atom has 11 protons. It is:
A. Magnesium
B. Sodium
C. Aluminium
D. Neon
Answer: B
Reason: Proton number 11 is sodium.

13) A neutral atom has 12 protons. Number of electrons is:
A. 10
B. 11
C. 12
D. 24
Answer: C
Reason: Neutral atoms have electrons = protons.

14) How many neutrons are in Image?
A. 11
B. 12
C. 23
D. 34
Answer: B
Reason: Neutrons = 23 − 11 = 12.

15) Which pair are isotopes?

Answer: B
Reason: Same protons (17) but different neutrons.

16) Isotopes of the same element have the same:
A. Mass number
B. Number of neutrons
C. Chemical properties
D. Physical properties always
Answer: C
Reason: Same electron arrangement gives same chemical behavior.

17) Which isotope has 8 neutrons and 8 protons?

Answer: A
Reason: Neutrons = 16 − 8 = 8.

18) Electronic configuration of sodium (11) is:
A. 2,8
B. 2,8,1
C. 2,8,2
D. 2,7,2
Answer: B
Reason: 11 electrons fill 2 then 8 then 1.

19) Electronic configuration of magnesium (12) is:
A. 2,8,2
B. 2,8,3
C. 2,7,3
D. 2,6,4
Answer: A
Reason: 12 electrons → 2,8,2.

20) Electronic configuration of neon (10) is:
A. 2,8
B. 2,7
C. 2,8,1
D. 2,8,8
Answer: A
Reason: 10 electrons fill first two shells.

21) Which element has configuration 2,6?
A. Carbon
B. Nitrogen
C. Oxygen
D. Fluorine
Answer: C
Reason: 2,6 is oxygen (8 electrons).

22) Which ion forms when sodium loses one electron?
A. Na⁻
B. Na²⁺
C. Na⁺
D. Na²⁻
Answer: C
Reason: Losing 1 electron makes +1 charge.

23) Electronic configuration of Na⁺ is:
A. 2,8,1
B. 2,8
C. 2,7
D. 2,8,2
Answer: B
Reason: Sodium loses outer electron → 10 electrons → 2,8.

24) Which ion forms when chlorine gains one electron?
A. Cl⁺
B. Cl²⁺
C. Cl⁻
D. Cl²⁻
Answer: C
Reason: Gaining 1 electron makes −1 charge.

25) Electronic configuration of Cl⁻ (17 + 1 electrons) is:
A. 2,8,7
B. 2,8,8
C. 2,7,8
D. 2,8,6
Answer: B
Reason: 18 electrons → 2,8,8.

26) Which group has a full outer shell?
A. Group I
B. Group II
C. Group VII
D. Group VIII (noble gases)
Answer: D
Reason: Noble gases have complete outer shell.

27) In Groups I–VII, group number equals:
A. Number of shells
B. Number of protons
C. Number of outer shell electrons
D. Number of neutrons
Answer: C
Reason: Group number matches valence electrons.

28) Period number equals:
A. Number of outer electrons
B. Number of occupied shells
C. Number of neutrons
D. Number of protons
Answer: B
Reason: Period tells how many shells are filled.

29) Which element is in Period 3 and has 1 outer electron?
A. Lithium
B. Sodium
C. Potassium
D. Hydrogen
Answer: B
Reason: Sodium is 2,8,1 (three shells, one outer electron).

30) An ionic bond is:
A. Sharing of electrons
B. Weak attraction between molecules
C. Strong electrostatic attraction between ions of opposite charge
D. Attraction between neutrons
Answer: C
Reason: Ionic bonding is electrostatic attraction of opposite ions.

31) Ionic bonding usually forms between:
A. Metal and metal
B. Non-metal and non-metal
C. Metal and non-metal
D. Noble gas and metal
Answer: C
Reason: Metals lose electrons, non-metals gain.

32) Which is a cation?
A. Cl⁻
B. O²⁻
C. Na⁺
D. Br⁻
Answer: C
Reason: Cations are positive ions.

33) Which is an anion?
A. Mg²⁺
B. Al³⁺
C. Na⁺
D. O²⁻
Answer: D
Reason: Anions are negative ions.

34) Sodium chloride forms when:
A. Na shares electrons with Cl
B. Na transfers 1 electron to Cl
C. Cl transfers 1 electron to Na
D. Na and Cl form a molecule with weak forces
Answer: B
Reason: Electron transfer creates Na⁺ and Cl⁻.

35) Ionic compounds are:
A. Low melting point liquids
B. High melting point solids
C. Always gases
D. Soft and easily compressed
Answer: B
Reason: Strong attractions in lattice need lots of energy to overcome.

36) Solid ionic compounds do not conduct electricity because:
A. They have no charges
B. Ions are fixed and cannot move
C. They contain only molecules
D. They have delocalised electrons
Answer: B
Reason: Charge carriers exist but are not mobile when solid.

37) Molten ionic compounds conduct electricity because:
A. Electrons move freely
B. Molecules carry charge
C. Ions are free to move
D. Neutrons move
Answer: C
Reason: Mobile ions carry current when molten.

38) A covalent bond is formed when:
A. Electrons are transferred
B. A pair of electrons is shared
C. Protons are shared
D. Neutrons are transferred
Answer: B
Reason: Covalent bonding involves sharing electrons.

39) Which molecule has a single covalent bond between identical atoms?
A. O₂
B. N₂
C. H₂
D. CO₂
Answer: C
Reason: H₂ shares one pair (single bond). O₂ is double, N₂ triple.

40) Water (H₂O) contains:
A. 1 covalent bond
B. 2 covalent bonds
C. 3 covalent bonds
D. 4 covalent bonds
Answer: B
Reason: Oxygen forms two single covalent bonds with two H atoms.

41) Methane (CH₄) contains:
A. 1 covalent bond
B. 2 covalent bonds
C. 3 covalent bonds
D. 4 covalent bonds
Answer: D
Reason: Carbon forms four single bonds.

42) Ammonia (NH₃) contains:
A. 1 covalent bond
B. 2 covalent bonds
C. 3 covalent bonds
D. 4 covalent bonds
Answer: C
Reason: Nitrogen forms three bonds and keeps one lone pair.

43) Simple molecular substances usually have low melting points because:
A. Covalent bonds are weak
B. Intermolecular forces are weak
C. Ions are mobile
D. They have giant lattices
Answer: B
Reason: Only weak forces between molecules are overcome.

44) Simple molecular substances do not conduct electricity because:
A. They have delocalised electrons
B. They contain mobile ions
C. They contain neutral molecules with no mobile charge carriers
D. They contain metal ions
Answer: C
Reason: No ions or free electrons to carry charge.

45) Diamond is hard because:
A. It has weak layers
B. It has strong covalent bonds in a 3D network
C. It has delocalised electrons
D. It is made of ions
Answer: B
Reason: Giant covalent lattice with many strong bonds.

46) Graphite conducts electricity because:
A. It contains ions
B. It contains delocalised electrons between layers
C. It has no electrons
D. It is an ionic lattice
Answer: B
Reason: One electron per carbon is delocalised and mobile.

47) Graphite is soft and slippery because:
A. Covalent bonds are weak inside layers
B. Layers are held together by weak forces and can slide
C. It has a 3D network
D. It has strong ionic bonds
Answer: B
Reason: Weak forces between layers allow sliding.

48) Silicon(IV) oxide (SiO₂) has:
A. Simple molecules only
B. A giant covalent structure
C. A metallic lattice
D. An ionic lattice
Answer: B
Reason: Si and O atoms form a continuous covalent network.

49) Metals conduct electricity because:
A. They have fixed ions only
B. They contain mobile delocalised electrons
C. They have only covalent bonds
D. They have weak intermolecular forces
Answer: B
Reason: Electron sea carries charge through lattice.

50) Metals are malleable because:
A. Metallic bonds break easily
B. Layers of ions can slide while electrons keep attraction
C. They contain brittle ionic lattices
D. They have only weak forces
Answer: B
Reason: Non-directional metallic bonding holds structure during sliding.

51) Which statement is always true for a neutral atom?
A. electrons = neutrons
B. electrons = protons
C. neutrons = protons
D. mass number = atomic number
Answer: B
Reason: Neutral means total charge is zero, so electrons equal protons.

52) An atom has proton number 9 and mass number 19. Neutrons =
A. 9
B. 10
C. 19
D. 28
Answer: B
Reason: Neutrons = 19 − 9 = 10.

53) Which pair has the same electronic configuration?
A. Na and Na⁺
B. Cl and Cl⁻
C. Mg²⁺ and Ne
D. O and O²⁻
Answer: C
Reason: Mg²⁺ has 10 electrons (2,8), same as neon.

54) Which species has 18 electrons?
A. Ar
B. Cl⁻
C. K⁺
D. All of the above
Answer: D
Reason: Ar = 18 e⁻, Cl⁻ = 17+1, K⁺ = 19−1.

55) Which statement about isotopes is correct?
A. different protons, same neutrons
B. same protons, different neutrons
C. same neutrons, different electrons
D. different protons, different electrons only
Answer: B
Reason: Isotopes differ in neutrons only.

56) Isotopes have the same chemical properties because they have the same:
A. mass number
B. number of neutrons
C. number and arrangement of electrons
D. density
Answer: C
Reason: Chemical reactions depend on electrons.

57) Which is a correct symbol interpretation?
For Image, the number of neutrons is:
A. 17
B. 20
C. 37
D. 54
Answer: B
Reason: 37 − 17 = 20.

58) A chloride ion is Image. Compared with a chlorine atom, it has:
A. one more proton
B. one fewer proton
C. one more electron
D. one fewer electron
Answer: C
Reason: Negative charge means gained an electron.

59) Which ion has the electronic configuration 2,8,8?
A. Na⁺
B. Cl⁻
C. Mg²⁺
D. Al³⁺
Answer: B
Reason: Cl⁻ has 18 electrons: 2,8,8.

60) Which particle contributes most to atomic mass?
A. electrons
B. protons and neutrons
C. electrons and protons
D. electrons and neutrons
Answer: B
Reason: Electrons have negligible mass.

61) Which statement about Period 3 is correct?
A. all elements have 3 outer electrons
B. all elements have 3 shells
C. all elements have 3 neutrons
D. all elements have 3 protons
Answer: B
Reason: Period number = number of occupied shells.

62) An element in Group VII is most likely to:
A. lose 1 electron
B. lose 2 electrons
C. gain 1 electron
D. gain 2 electrons
Answer: C
Reason: Group VII has 7 outer electrons, gains 1 to complete shell.

63) Which has a full outer shell?
A. Na
B. Ne
C. Cl
D. Mg
Answer: B
Reason: Noble gases have full outer shells.

64) An atom has configuration 2,8,3. Its group is:
A. I
B. III
C. V
D. VIII
Answer: B
Reason: 3 outer electrons means Group III (I to VII rule).

65) An element with configuration 2,8,8,2 is in:
A. Period 2
B. Period 3
C. Period 4
D. Period 8
Answer: C
Reason: Four shells occupied.

66) Which is a compound but NOT a mixture?
A. air
B. seawater
C. carbon dioxide
D. brass
Answer: C
Reason: CO₂ is chemically combined, fixed ratio.

67) Which is a mixture of metals?
A. sodium chloride
B. diamond
C. brass
D. carbon dioxide
Answer: C
Reason: Brass is an alloy (mixture).

68) Which change is chemical?
A. melting ice
B. boiling water
C. dissolving sugar in water
D. burning magnesium
Answer: D
Reason: New substance forms (MgO).

69) Which method separates a mixture based on different boiling points?
A. filtration
B. crystallisation
C. fractional distillation
D. chromatography
Answer: C
Reason: Uses boiling point differences.

70) A compound differs from a mixture because a compound:
A. can be separated physically
B. has fixed composition
C. always conducts electricity
D. always exists as molecules
Answer: B
Reason: Compounds have fixed ratios.

71) An ionic bond is best described as:
A. attraction between nuclei and shared electrons
B. attraction between opposite ions
C. attraction between molecules
D. attraction between atoms in a layer
Answer: B
Reason: Ionic bonding is electrostatic between ions.

72) Which pair most likely forms an ionic compound?
A. carbon and oxygen
B. sodium and chlorine
C. hydrogen and chlorine
D. nitrogen and hydrogen
Answer: B
Reason: Metal + non-metal gives ionic.

73) Which statement about solid ionic compounds is correct?
A. they conduct electricity because ions move freely
B. they do not conduct because ions are fixed
C. they conduct because electrons move freely
D. they conduct because molecules carry charge
Answer: B
Reason: Ions cannot move when solid.

74) Ionic compounds conduct when molten because:
A. electrons become delocalised
B. ions are free to move
C. covalent bonds break into electrons
D. atoms become neutral molecules
Answer: B
Reason: Mobile ions carry charge.

75) Which is the BEST evidence for ions in a molten ionic substance?
A. it is shiny
B. it conducts electricity when molten
C. it melts at low temperature
D. it is soft
Answer: B
Reason: Conduction needs moving charged particles.

76) In a dot-and-cross diagram for NaCl, the transferred electron ends up:
A. in sodium’s outer shell
B. in chlorine’s outer shell
C. in sodium’s nucleus
D. shared between both atoms
Answer: B
Reason: Na transfers electron to Cl.

77) Magnesium forms Mg²⁺ because it:
A. gains 2 electrons
B. loses 1 electron
C. loses 2 electrons
D. shares 2 electrons
Answer: C
Reason: Two outer electrons are lost.

78) Oxygen forms O²⁻ because it:
A. loses 2 electrons
B. gains 2 electrons
C. shares 2 electrons only
D. gains 1 electron
Answer: B
Reason: Needs 2 electrons to complete shell.

79) Which ionic formula is correct for magnesium chloride?
A. MgCl
B. MgCl₂
C. Mg₂Cl
D. Mg₂Cl₂
Answer: B
Reason: Mg²⁺ needs two Cl⁻ to balance.

80) Which ionic compound has ions with charges +2 and −1?
A. NaCl
B. MgO
C. CaCl₂
D. Al₂O₃
Answer: C
Reason: Ca²⁺ and Cl⁻.

81) A covalent bond forms when:
A. electrons are transferred
B. electrons are shared as a pair
C. protons are shared
D. neutrons are transferred
Answer: B
Reason: Definition of covalent bond.

82) Which molecule contains a double covalent bond?
A. H₂
B. Cl₂
C. O₂
D. CH₄
Answer: C
Reason: O₂ shares two pairs.

83) Which molecule contains a triple covalent bond?
A. N₂
B. CO₂
C. H₂O
D. HCl
Answer: A
Reason: N₂ has three shared pairs.

84) Carbon dioxide is best described as:
A. ionic lattice
B. simple molecules with covalent bonds
C. giant covalent structure
D. metallic lattice
Answer: B
Reason: CO₂ exists as separate molecules.

85) Simple molecular substances generally have low boiling points because:
A. covalent bonds are weak
B. intermolecular forces are weak
C. ions are weakly bonded
D. electrons are delocalised
Answer: B
Reason: Only weak forces between molecules break.

86) Diamond does not conduct electricity because:
A. it has ions fixed in a lattice
B. it has no electrons
C. all outer electrons are used in covalent bonds
D. it has weak intermolecular forces
Answer: C
Reason: No mobile charge carriers.

87) Graphite conducts electricity because:
A. it contains ions
B. it has delocalised electrons
C. it is molten at room temperature
D. it has weak covalent bonds
Answer: B
Reason: One electron per carbon is delocalised.

88) Graphite is soft because:
A. covalent bonds within layers are weak
B. layers are held by weak forces and slide
C. it has no layers
D. it is ionic
Answer: B
Reason: Weak forces between layers allow sliding.

89) Silicon(IV) oxide has a high melting point because:
A. it contains small molecules
B. it has weak forces between molecules
C. it has many strong covalent bonds in a network
D. it has delocalised electrons
Answer: C
Reason: Giant covalent network.

90) Which two substances are giant covalent?
A. diamond and sodium chloride
B. diamond and graphite
C. graphite and water
D. silicon dioxide and magnesium oxide
Answer: B
Reason: Both are carbon networks.

91) Metallic bonding involves:
A. sharing electrons between non-metals
B. transfer of electrons to form ions only
C. attraction between positive ions and delocalised electrons
D. weak forces between molecules
Answer: C
Reason: Definition of metallic bonding.

92) Metals are malleable because:
A. layers of ions can slide and bonding remains
B. they contain rigid ionic lattices
C. covalent bonds break and reform
D. they have weak intermolecular forces
Answer: A
Reason: Non-directional bonding holds structure.

93) Metals conduct electricity because:
A. ions move freely in solid metal
B. delocalised electrons move through the lattice
C. atoms carry charge
D. neutrons carry charge
Answer: B
Reason: Mobile electrons carry current.

94) Which substance is most likely to be a good conductor as a solid?
A. sodium chloride
B. diamond
C. copper
D. carbon dioxide
Answer: C
Reason: Metals conduct as solids.

95) Which is a correct comparison?
A. ionic solids conduct, metals do not
B. metals are brittle, ionic solids are malleable
C. ionic solids are brittle, metals are malleable
D. covalent molecules conduct well
Answer: C
Reason: Ionic lattices shatter when layers shift; metals bend.

96) Which statement about “number of electrons” is correct?
A. changing electrons changes the element
B. changing protons changes the element
C. changing neutrons changes the element
D. changing electrons changes mass number
Answer: B
Reason: Element identity depends on protons.

97) An aluminium atom (2,8,3) forms Al³⁺ with configuration:
A. 2,8,3
B. 2,8
C. 2,7
D. 2,8,1
Answer: B
Reason: Loses 3 electrons, leaving 10 (2,8).

98) Which has the greatest number of neutrons?

Answer: D
Reason: Neutrons: 6, 8, 12, 18. Largest is 18.

99) Which statement is true about a mixture?
A. fixed ratio
B. new substance forms
C. components keep their properties
D. can only be separated chemically
Answer: C
Reason: Mixture components retain properties.

100) Which statement best links structure to conductivity?
A. graphite conducts because it is ionic
B. diamond conducts because it is carbon
C. graphite conducts because it has mobile delocalised electrons
D. silicon dioxide conducts because it has ions
Answer: C
Reason: Conductivity depends on mobile charge carriers.

Thank You!

Sana Shariq

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