Classification of Elements MCQs – Periodic Table Class 11
Classification of Elements MCQs – Periodic Table Class 11
Course: CBSE Class 11 Chemistry – MCQs with Answers and Explanations
Section: Physical Chemistry – MCQ Titles
The following 50 MCQs are strictly based on the NCERT chapter “Classification of Elements and Periodicity in Properties”. Questions are arranged section-wise to ensure complete syllabus coverage and include clear, concept-building explanations, making them ideal for CBSE Class 11 board exam preparation.
Section A: Historical Development of Periodic Classification
1. The first attempt to classify elements was made by
A. Mendeleev
B. Dobereiner
C. Newlands
D. Moseley
Answer: B
Explanation: Dobereiner proposed the Law of Triads, grouping elements with similar properties.
2. Dobereiner’s triads were based on similarity in
A. atomic numbers
B. atomic masses
C. physical and chemical properties
D. valency only
Answer: C
Explanation: Elements in a triad showed similar properties and a mass relationship.
3. In Dobereiner’s triad, the atomic mass of the middle element is approximately
A. sum of other two
B. difference of other two
C. average of other two
D. product of other two
Answer: C
Explanation: This was the basis of Dobereiner’s law.
4. The Law of Octaves was proposed by
A. Mendeleev
B. Dobereiner
C. Moseley
D. Newlands
Answer: D
Explanation: Newlands arranged elements by increasing atomic mass.
5. Law of Octaves states that every
A. 6th element repeats properties
B. 7th element repeats properties
C. 8th element repeats properties
D. 9th element repeats properties
Answer: C
Explanation: Properties repeat after every eight elements.
Section B: Mendeleev’s Periodic Table
6. Mendeleev arranged elements on the basis of
A. atomic number
B. atomic mass
C. valency
D. density
Answer: B
Explanation: Mendeleev’s periodic law was based on atomic mass.
7. Mendeleev’s periodic law states that properties of elements are periodic functions of
A. atomic number
B. atomic mass
C. valency
D. density
Answer: B
Explanation: This was the original periodic law.
8. Mendeleev left gaps in his periodic table to
A. adjust atomic masses
B. maintain periodicity
C. predict new elements
D. remove anomalies
Answer: C
Explanation: He predicted undiscovered elements like gallium and germanium.
9. Eka-aluminium predicted by Mendeleev was later discovered as
A. boron
B. aluminium
C. gallium
D. indium
Answer: C
Explanation: Eka-aluminium corresponds to gallium.
10. Which was a major drawback of Mendeleev’s periodic table?
A. No noble gases
B. Wrong atomic masses
C. Position of hydrogen
D. All of these
Answer: D
Explanation: Several limitations existed, including hydrogen’s position.
Section C: Modern Periodic Law and Table
11. Modern periodic law is based on
A. atomic mass
B. atomic number
C. valency
D. atomic size
Answer: B
Explanation: Moseley established atomic number as the basis.
12. Modern periodic law was proposed by
A. Mendeleev
B. Newlands
C. Moseley
D. Dobereiner
Answer: C
Explanation: Moseley correlated atomic number with properties.
13. The modern periodic table contains
A. 7 periods and 16 groups
B. 8 periods and 18 groups
C. 7 periods and 18 groups
D. 9 periods and 18 groups
Answer: C
Explanation: Standard modern periodic table structure.
14. Elements in the same group have the same
A. atomic mass
B. atomic number
C. number of shells
D. valence electrons
Answer: D
Explanation: Valence electrons determine chemical properties.
15. Period number indicates the number of
A. valence electrons
B. neutrons
C. shells
D. protons
Answer: C
Explanation: Period number equals number of electron shells.
Section D: Electronic Configuration and Periodicity
16. The cause of periodicity in properties is
A. atomic mass
B. nuclear charge
C. electronic configuration
D. atomic volume
Answer: C
Explanation: Similar valence shell configurations cause periodic trends.
17. Which block contains elements with valence electrons in s-subshell?
A. s-block
B. p-block
C. d-block
D. f-block
Answer: A
Explanation: s-block elements have outer electrons in s-orbitals.
18. Alkali metals belong to
A. Group 1
B. Group 2
C. Group 17
D. Group 18
Answer: A
Explanation: Group 1 elements are alkali metals.
19. Halogens belong to
A. Group 16
B. Group 17
C. Group 18
D. Group 15
Answer: B
Explanation: Group 17 elements are halogens.
20. Noble gases are placed in
A. Group 16
B. Group 17
C. Group 18
D. Group 0
Answer: C
Explanation: Modern table places noble gases in Group 18.
Section E: Atomic Radius and Ionic Radius
21. Atomic radius decreases across a period due to
A. increase in shells
B. increase in nuclear charge
C. decrease in electrons
D. shielding effect
Answer: B
Explanation: Greater nuclear charge pulls electrons closer.
22. Atomic radius increases down a group due to
A. increase in nuclear charge
B. decrease in shielding
C. increase in shells
D. increase in valence electrons
Answer: C
Explanation: Additional shells increase size.
23. Cations are smaller than parent atoms because
A. loss of electrons increases nuclear pull
B. gain of electrons
C. increase in shells
D. decrease in protons
Answer: A
Explanation: Effective nuclear charge increases.
24. Anions are larger than parent atoms due to
A. loss of electrons
B. decrease in repulsion
C. increase in electron-electron repulsion
D. increase in nuclear charge
Answer: C
Explanation: Extra electrons increase repulsion.
25. Which has the smallest size?
A. Na
B. Na⁺
C. Cl
D. Cl⁻
Answer: B
Explanation: Cations are smaller than neutral atoms.
Section F: Ionization Enthalpy
26. Ionization enthalpy is the energy required to
A. gain an electron
B. lose an electron
C. break nucleus
D. form ion
Answer: B
Explanation: It refers to removal of the outermost electron.
27. Ionization enthalpy increases across a period due to
A. increasing atomic size
B. decreasing nuclear charge
C. increasing nuclear charge
D. shielding effect
Answer: C
Explanation: Stronger attraction makes electron removal difficult.
28. Ionization enthalpy decreases down a group because of
A. increased nuclear charge
B. increased atomic size
C. decreased shielding
D. increased electronegativity
Answer: B
Explanation: Outer electrons are farther from nucleus.
29. Which element has the highest ionization enthalpy?
A. Na
B. Mg
C. Cl
D. Ne
Answer: D
Explanation: Noble gases have maximum ionization enthalpy.
30. Successive ionization enthalpy increases due to
A. loss of protons
B. reduced nuclear charge
C. increased attraction on remaining electrons
D. electron gain
Answer: C
Explanation: Remaining electrons experience stronger attraction.
Section G: Electron Gain Enthalpy and Electronegativity
31. Electron gain enthalpy is associated with
A. loss of electron
B. gain of electron
C. sharing of electrons
D. nuclear reactions
Answer: B
Explanation: It involves acceptance of an electron.
32. Halogens have high electron gain enthalpy because
A. large size
B. stable noble gas configuration
C. need one electron to complete octet
D. low nuclear charge
Answer: C
Explanation: They readily gain one electron.
33. Electron gain enthalpy becomes less negative down a group due to
A. increased nuclear charge
B. increased atomic size
C. increased valence electrons
D. decreased shielding
Answer: B
Explanation: Larger size reduces attraction for incoming electron.
34. Electronegativity is the tendency to
A. lose electrons
B. gain protons
C. attract shared electrons
D. repel electrons
Answer: C
Explanation: It measures attraction for bonded electrons.
35. Most electronegative element is
A. oxygen
B. nitrogen
C. chlorine
D. fluorine
Answer: D
Explanation: Fluorine has highest electronegativity.
Section H: Valency and Chemical Reactivity
36. Valency of group 1 elements is
A. 0
B. 1
C. 2
D. 7
Answer: B
Explanation: They lose one electron to form cations.
37. Valency across a period first increases then
A. remains constant
B. decreases
C. becomes zero
D. increases indefinitely
Answer: B
Explanation: After group 14, valency decreases.
38. Reactivity of alkali metals increases down the group because
A. ionization enthalpy increases
B. atomic size decreases
C. ionization enthalpy decreases
D. electronegativity increases
Answer: C
Explanation: Easier loss of valence electron.
39. Reactivity of halogens decreases down the group due to
A. decreasing size
B. increasing size
C. increasing electron gain enthalpy
D. increasing electronegativity
Answer: B
Explanation: Larger atoms attract electrons less strongly.
40. Which element is most metallic?
A. Li
B. Na
C. K
D. Cs
Answer: D
Explanation: Metallic character increases down the group.
Section I: Conceptual NCERT-Based MCQs
41. Periodic trends are repeated due to
A. repetition of atomic masses
B. repetition of atomic numbers
C. repetition of electronic configuration
D. repetition of shells only
Answer: C
Explanation: Valence shell configuration repeats periodically.
42. Which block contains transition elements?
A. s-block
B. p-block
C. d-block
D. f-block
Answer: C
Explanation: Transition metals belong to d-block.
43. Lanthanoids and actinoids belong to
A. s-block
B. p-block
C. d-block
D. f-block
Answer: D
Explanation: They involve filling of f-orbitals.
44. Which element shows diagonal relationship with magnesium?
A. Boron
B. Aluminium
C. Silicon
D. Beryllium
Answer: A
Explanation: Boron and magnesium show diagonal similarity.
45. Periodicity in chemical properties is absent in
A. metals
B. non-metals
C. noble gases
D. hydrogen
Answer: C
Explanation: Noble gases are chemically inert.
46. The modern periodic table is superior because it is based on
A. mass
B. density
C. atomic number
D. atomic volume
Answer: C
Explanation: Atomic number removes anomalies.
47. Which pair shows similar properties?
A. Na and K
B. Na and Mg
C. O and N
D. Cl and S
Answer: A
Explanation: Same group elements show similar properties.
48. Shielding effect increases down a group due to
A. increased nuclear charge
B. increased number of shells
C. increased electronegativity
D. decreased atomic size
Answer: B
Explanation: More inner shells block nuclear attraction.
49. Metallic character decreases across a period due to
A. increasing size
B. decreasing ionization enthalpy
C. increasing nuclear charge
D. increasing shielding
Answer: C
Explanation: Stronger nuclear attraction reduces metallic nature.
50. Which property shows the maximum variation in periodic table?
A. Valency
B. Atomic radius
C. Ionization enthalpy
D. Electronegativity
Answer: B
Explanation: Atomic size varies significantly across periods and groups.
✅ Completion Note
This completes a fully NCERT-aligned, CBSE-standard set of 50 MCQs on Classification of Elements and Periodicity, ideal for concept clarity, revision, and board exam practice.