Periodic Classification of Elements Part 4: MCQs (Q76–Q100)
📘 Periodic Classification of Elements – MCQs
🔹 Part 4: Questions 76–100
Q76. Which of the following is the most reactive alkali metal?
A) Lithium
B) Sodium
C) Potassium
D) Cesium
Correct Answer: D) Cesium
Explanation:
- A) Lithium → Least reactive in Group 1.
- B) Sodium → More reactive than Li, but less than Cs.
- C) Potassium → More reactive than Na, but less than Cs.
- ✅ D) Cesium → Largest atom, easiest to lose e⁻, most reactive.
Q77. Which of the following is the most reactive halogen?
A) Fluorine
B) Chlorine
C) Bromine
D) Iodine
Correct Answer: A) Fluorine
Explanation:
- ✅ A) Fluorine → Highest electronegativity, strongest tendency to gain e⁻.
- B) Chlorine, C) Bromine, D) Iodine → Decreasing reactivity down the group.
Q78. The correct order of atomic size in Group 1 elements is:
A) Li < Na < K < Rb < Cs
B) Cs < Rb < K < Na < Li
C) Na < Li < K < Cs < Rb
D) K < Na < Li < Cs < Rb
Correct Answer: A) Li < Na < K < Rb < Cs
Explanation:
- ✅ A) Atomic size increases down a group → smallest Li, largest Cs.
- B, C, D → Wrong sequences.
Q79. The correct order of reactivity of Group 17 elements is:
A) I > Br > Cl > F
B) Br > Cl > I > F
C) F > Cl > Br > I
D) Cl > F > Br > I
Correct Answer: C) F > Cl > Br > I
Explanation:
- ✅ C) Reactivity decreases down the group → Fluorine most reactive.
- A, B, D → Wrong trends.
Q80. Which of the following is a transition element?
A) Zn
B) K
C) Na
D) Ca
Correct Answer: A) Zn
Explanation:
- ✅ A) Zn → d-block, transition element (though chemically less typical).
- B) K → Group 1.
- C) Na → Group 1.
- D) Ca → Group 2.
Q81. Which of the following is a noble gas with only 2 electrons?
A) Helium
B) Neon
C) Argon
D) Krypton
Correct Answer: A) Helium
Explanation:
- ✅ A) Helium → 1s², stable with 2 electrons.
- B, C, D → Have 8 electrons in outer shell.
Q82. Which element shows properties of both metals and non-metals?
A) Carbon
B) Sodium
C) Boron
D) Oxygen
Correct Answer: C) Boron
Explanation:
- A) Carbon → Non-metal.
- B) Sodium → Metal.
- ✅ C) Boron → Metalloid.
- D) Oxygen → Non-metal.
Q83. Which of the following oxides is amphoteric?
A) Na₂O
B) MgO
C) Al₂O₃
D) CO₂
Correct Answer: C) Al₂O₃
Explanation:
- A) Na₂O → Basic oxide.
- B) MgO → Basic oxide.
- ✅ C) Al₂O₃ → Amphoteric, reacts with both acids & bases.
- D) CO₂ → Acidic oxide.
Q84. Which element has electronic configuration 2,8,8,1?
A) Na
B) K
C) Ca
D) Rb
Correct Answer: B) K (Potassium)
Explanation:
- A) Na → 2,8,1.
- ✅ B) K → 2,8,8,1 (Z=19).
- C) Ca → 2,8,8,2.
- D) Rb → 2,8,18,8,1.
Q85. Which of the following belongs to Period 3, Group 16?
A) Oxygen
B) Sulphur
C) Chlorine
D) Sodium
Correct Answer: B) Sulphur
Explanation:
- A) Oxygen → Period 2, Group 16.
- ✅ B) Sulphur → Period 3, Group 16.
- C) Chlorine → Group 17.
- D) Sodium → Group 1.
Q86. Which element among the following is a halogen?
A) Oxygen
B) Nitrogen
C) Chlorine
D) Neon
Correct Answer: C) Chlorine
Explanation:
- A) Oxygen → Group 16.
- B) Nitrogen → Group 15.
- ✅ C) Chlorine → Group 17 halogen.
- D) Neon → Group 18.
Q87. Which element has the highest ionization enthalpy in Period 2?
A) Lithium
B) Beryllium
C) Fluorine
D) Neon
Correct Answer: D) Neon
Explanation:
- A, B, C → Lower ionization enthalpy.
- ✅ D) Neon → Noble gas, smallest size, most stable.
Q88. Which of the following pairs are isotopes?
A) ¹²C and ¹⁴N
B) ¹²C and ¹³C
C) ¹H and ²He
D) ¹⁶O and ¹⁹F
Correct Answer: B) ¹²C and ¹³C
Explanation:
- A, C, D → Different elements.
- ✅ B) Isotopes → Same element (C), different masses.
Q89. Which of the following was a limitation of Mendeleev’s periodic table?
A) No space for new elements
B) Position of isotopes not explained
C) Arranged by atomic number
D) Classification of metals and non-metals
Correct Answer: B) Position of isotopes not explained
Explanation:
- A) He left spaces for new elements → Strength, not limitation.
- ✅ B) Isotopes → Could not be placed properly.
- C) He arranged by atomic mass, not number.
- D) Metals/non-metals were arranged correctly.
Q90. Which of the following is the most metallic element in Period 3?
A) Sodium
B) Magnesium
C) Aluminum
D) Chlorine
Correct Answer: A) Sodium
Explanation:
- ✅ A) Sodium → Leftmost in period, most metallic.
- B, C, D → Metallic character decreases across the period.
Q91. Which of the following is the least metallic in Period 3?
A) Sodium
B) Aluminum
C) Sulphur
D) Chlorine
Correct Answer: D) Chlorine
Explanation:
- ✅ D) Chlorine → Halogen, highly non-metallic.
- Others → More metallic than chlorine.
Q92. The modern periodic law is based on:
A) Atomic mass
B) Atomic number
C) Number of neutrons
D) Mass number
Correct Answer: B) Atomic number
Explanation:
- A) Mendeleev used atomic mass.
- ✅ B) Moseley → Modern law based on atomic number.
- C & D → Not correct basis.
Q93. Which of the following elements will have similar chemical properties as oxygen?
A) Nitrogen
B) Sulphur
C) Chlorine
D) Neon
Correct Answer: B) Sulphur
Explanation:
- ✅ B) Sulphur → Same group (16), similar properties.
- A, C, D → Different groups.
Q94. Which element has configuration 2,8,6?
A) Carbon
B) Oxygen
C) Sulphur
D) Neon
Correct Answer: C) Sulphur
Explanation:
- A) Carbon → 2,4.
- B) Oxygen → 2,6.
- ✅ C) Sulphur → 2,8,6 (Z=16).
- D) Neon → 2,8.
Q95. Which of the following is a property of non-metals?
A) They are ductile
B) They are malleable
C) They are brittle
D) They are good conductors
Correct Answer: C) They are brittle
Explanation:
- A, B → Metals.
- ✅ C) Non-metals are brittle, break on hammering.
- D) Conductors → Metals.
Q96. Which of the following increases down a group?
A) Ionization energy
B) Atomic size
C) Electronegativity
D) Non-metallic character
Correct Answer: B) Atomic size
Explanation:
- A) Ionization energy → Decreases.
- ✅ B) Atomic size → Increases due to new shells.
- C) EN → Decreases.
- D) Non-metallic character → Decreases.
Q97. Which of the following decreases across a period?
A) Ionization energy
B) Electronegativity
C) Atomic radius
D) Non-metallic character
Correct Answer: C) Atomic radius
Explanation:
- A) IE → Increases.
- B) EN → Increases.
- ✅ C) Atomic radius → Decreases due to greater nuclear pull.
- D) Non-metallic character → Increases.
Q98. Which group contains elements with completely filled valence shells?
A) Group 1
B) Group 16
C) Group 17
D) Group 18
Correct Answer: D) Group 18
Explanation:
- A, B, C → Incomplete valence shells.
- ✅ D) Group 18 → Noble gases, filled shells.
Q99. Which of the following is NOT a metalloid?
A) Boron
B) Silicon
C) Arsenic
D) Calcium
Correct Answer: D) Calcium
Explanation:
- A, B, C → Metalloids.
- ✅ D) Calcium → Alkaline earth metal.
Q100. Which property of elements was used by Mendeleev to arrange his periodic table?
A) Atomic number
B) Atomic mass
C) Mass number
D) Number of neutrons
Correct Answer: B) Atomic mass
Explanation:
- ✅ B) Mendeleev → Arranged by atomic mass.
- A) Atomic number → Modern periodic table.
- C, D → Not used in arrangement.
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