Periodic Classification of Elements Part 1: MCQs (Q1–Q25)
📘 Periodic Classification of Elements – MCQs
🔹 Part 1: Questions 1–25
Q1. Who is considered the “Father of Modern Periodic Table”?
A) Newlands
B) Mendeleev
C) Dobereiner
D) Moseley
Correct Answer: D) Moseley
Explanation:
- A) Newlands → Gave the Law of Octaves, but it failed after calcium.
- B) Mendeleev → Proposed the first successful periodic table, arranged by atomic mass.
- C) Dobereiner → Suggested triads of elements, but it was incomplete.
- ✅ D) Moseley → Correct, he arranged elements by atomic number, leading to the modern periodic table.
Q2. The modern periodic law states that the properties of elements are periodic functions of their:
A) Atomic mass
B) Atomic number
C) Valency
D) Number of neutrons
Correct Answer: B) Atomic number
Explanation:
- A) Atomic mass → Used by Mendeleev, but failed for some elements (e.g., cobalt & nickel).
- ✅ B) Atomic number → Correct, as per Moseley’s modern law.
- C) Valency → Valency changes periodically but is not the fundamental basis.
- D) Number of neutrons → Does not determine periodic properties.
Q3. Which of the following is NOT a limitation of Mendeleev’s periodic table?
A) Position of isotopes
B) Uncertainty about hydrogen
C) Increasing atomic number not followed
D) Classification of metals and non-metals
Correct Answer: D) Classification of metals and non-metals
Explanation:
- A) Isotopes → Mendeleev placed isotopes separately though they have similar properties.
- B) Hydrogen → Could be placed in group 1 or 17, creating confusion.
- C) Atomic number → He arranged by atomic mass, not atomic number.
- ✅ D) Metals & non-metals → He classified them well into groups. Not a limitation.
Q4. The Law of Octaves was given by:
A) Dobereiner
B) Mendeleev
C) Moseley
D) Newlands
Correct Answer: D) Newlands
Explanation:
- A) Dobereiner → Proposed triads, not octaves.
- B) Mendeleev → Proposed periodic law of atomic mass.
- C) Moseley → Proposed atomic number law.
- ✅ D) Newlands → Correct, he noticed repetition of properties after every 8th element.
Q5. In Dobereiner’s triads, the atomic mass of the middle element is:
A) Double of the first element
B) Average of first and third
C) Equal to first element
D) Average of isotopes
Correct Answer: B) Average of first and third
Explanation:
- A) Double → Incorrect.
- ✅ B) Average → Correct, e.g., (Li + K)/2 ≈ Na.
- C) Equal → Wrong.
- D) Isotopes → Not related to triads.
Q6. Which of the following pairs of elements was a problem in Mendeleev’s table?
A) H and He
B) Co and Ni
C) Na and Mg
D) N and O
Correct Answer: B) Co and Ni
Explanation:
- A) H & He → Hydrogen’s position was uncertain, but helium was not known then.
- ✅ B) Co & Ni → Atomic masses did not follow the order, but properties did.
- C) Na & Mg → Properly placed.
- D) N & O → Properly placed.
Q7. Which element is placed in Group 1 but also resembles Group 17?
A) Helium
B) Sodium
C) Hydrogen
D) Lithium
Correct Answer: C) Hydrogen
Explanation:
- A) Helium → Noble gas, in group 18.
- B) Sodium → Group 1 only.
- ✅ C) Hydrogen → Resembles alkali metals (forms H⁺) and halogens (forms H⁻).
- D) Lithium → Strictly group 1.
Q8. The Modern Periodic Table is divided into:
A) Groups and Rows
B) Rows and Columns
C) Periods and Groups
D) Periods and Families
Correct Answer: C) Periods and Groups
Explanation:
- A & B) Rows/Columns → Informal names.
- ✅ C) Periods (horizontal) & Groups (vertical) → Correct classification.
- D) Families → Old term for groups.
Q9. How many periods are there in the Modern Periodic Table?
A) 7
B) 8
C) 6
D) 9
Correct Answer: A) 7
Explanation:
- ✅ A) 7 → Correct, 7 horizontal rows.
- B) 8 → Wrong.
- C) 6 → Older periodic table.
- D) 9 → Not correct.
Q10. How many groups are there in the Modern Periodic Table?
A) 7
B) 18
C) 8
D) 10
Correct Answer: B) 18
Explanation:
- A) 7 → Periods, not groups.
- ✅ B) 18 → Correct, 18 vertical columns.
- C) 8 → Only Mendeleev’s table had 8 groups.
- D) 10 → Wrong.
Q11. Which of the following is a noble gas?
A) Fluorine
B) Neon
C) Oxygen
D) Nitrogen
Correct Answer: B) Neon
Explanation:
- A) Fluorine → Halogen, group 17.
- ✅ B) Neon → Noble gas, group 18.
- C) Oxygen → Chalcogen.
- D) Nitrogen → P-block, but not noble.
Q12. Elements in the same group have:
A) Same atomic mass
B) Same number of valence electrons
C) Same physical state
D) Same period number
Correct Answer: B) Same number of valence electrons
Explanation:
- A) Atomic mass → Increases down group.
- ✅ B) Valence electrons → Define group properties.
- C) Physical state → Not always same (e.g., halogens).
- D) Period → Same group, but different periods.
Q13. Which of the following is an alkali metal?
A) Calcium
B) Magnesium
C) Sodium
D) Aluminum
Correct Answer: C) Sodium
Explanation:
- A) Calcium → Alkaline earth metal.
- B) Magnesium → Alkaline earth metal.
- ✅ C) Sodium → Group 1, alkali metal.
- D) Aluminum → Group 13.
Q14. Which of the following is the most reactive non-metal?
A) Oxygen
B) Fluorine
C) Chlorine
D) Iodine
Correct Answer: B) Fluorine
Explanation:
- A) Oxygen → Reactive but not most.
- ✅ B) Fluorine → Most electronegative, most reactive.
- C) Chlorine → Less reactive than fluorine.
- D) Iodine → Least reactive among halogens.
Q15. Which of the following is the least reactive alkali metal?
A) Lithium
B) Sodium
C) Potassium
D) Cesium
Correct Answer: A) Lithium
Explanation:
- ✅ A) Lithium → Reactivity increases down group 1, so lithium is least reactive.
- B) Sodium, C) Potassium, D) Cesium → More reactive than lithium.
Q16. Across a period, the atomic size:
A) Increases
B) Decreases
C) Remains same
D) First increases then decreases
Correct Answer: B) Decreases
Explanation:
- A) Increases → Wrong, nuclear charge increases.
- ✅ B) Decreases → Due to higher nuclear pull.
- C) Same → Wrong.
- D) First increases then decreases → Not true for atomic size.
Q17. Down a group, the atomic size:
A) Increases
B) Decreases
C) Remains same
D) Irregular
Correct Answer: A) Increases
Explanation:
- ✅ A) Increases → Due to addition of new shells.
- B) Decreases → Wrong.
- C) Same → Wrong.
- D) Irregular → Wrong.
Q18. Across a period, metallic character:
A) Increases
B) Decreases
C) Remains constant
D) Irregular
Correct Answer: B) Decreases
Explanation:
- A) Increases → Opposite trend.
- ✅ B) Decreases → Non-metallic character increases across period.
- C & D → Wrong.
Q19. Down a group, metallic character:
A) Increases
B) Decreases
C) Constant
D) Irregular
Correct Answer: A) Increases
Explanation:
- ✅ A) Increases → Due to easier loss of electrons (low ionization energy).
- B, C, D → Wrong.
Q20. Across a period, electronegativity:
A) Increases
B) Decreases
C) Remains same
D) Irregular
Correct Answer: A) Increases
Explanation:
- ✅ A) Increases → Due to higher nuclear charge.
- B) Decreases → Wrong.
- C, D → Wrong.
Q21. Down a group, electronegativity:
A) Increases
B) Decreases
C) Constant
D) Irregular
Correct Answer: B) Decreases
Explanation:
- A) Increases → Wrong.
- ✅ B) Decreases → Because outer electrons are farther from nucleus.
- C, D → Wrong.
Q22. Which of the following belongs to Group 17?
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 noble gas.
Q23. Which of the following belongs to Group 2 (alkaline earth metal)?
A) Sodium
B) Magnesium
C) Potassium
D) Iron
Correct Answer: B) Magnesium
Explanation:
- A) Sodium → Group 1.
- ✅ B) Magnesium → Group 2.
- C) Potassium → Group 1.
- D) Iron → Transition element.
Q24. The outermost configuration of Group 1 elements is:
A) ns²
B) ns¹
C) ns²np⁵
D) ns²np⁶
Correct Answer: B) ns¹
Explanation:
- ✅ B) ns¹ → One valence electron in s-orbital.
- A) ns² → Group 2 elements.
- C) ns²np⁵ → Group 17.
- D) ns²np⁶ → Group 18.
Q25. Which element in Period 3 has the largest atomic size?
A) Sodium
B) Magnesium
C) Aluminum
D) Chlorine
Correct Answer: A) Sodium
Explanation:
- ✅ A) Sodium → Atomic size decreases across period, so leftmost (Na) is largest.
- B, C, D → Smaller than sodium.
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