Classification of Elements MCQs – Periodicity Class 11
Classification of Elements MCQs – Periodicity (Class 11 Chemistry)
Course: CBSE Class 11 Chemistry – MCQs with Answers and Explanations
Section: Inorganic Chemistry – MCQ Titles
The following 50 Multiple Choice Questions (MCQs) are strictly based on the NCERT chapter “Classification of Elements and Periodicity in Properties”. The questions are arranged section-wise to ensure complete syllabus coverage, with clear, concept-clearing explanations, making them ideal for CBSE Class 11 board exam preparation.
Section A: Introduction to Periodic Classification
1. The need for classification of elements arose mainly to
A. increase atomic masses
B. study radioactive elements
C. simplify the study of properties of elements
D. prepare compounds
Answer: C
Explanation: Classification helps in systematic study and prediction of properties.
2. The modern periodic table is based on
A. atomic mass
B. atomic volume
C. atomic number
D. valency
Answer: C
Explanation: Moseley showed that atomic number is the fundamental property.
3. The total number of elements known today is approximately
A. 92
B. 103
C. 118
D. 120
Answer: C
Explanation: At present, 118 elements are known.
Section B: Historical Development of Periodic Table
4. Dobereiner proposed the concept of
A. octaves
B. triads
C. periodic law
D. atomic number
Answer: B
Explanation: Dobereiner grouped elements in sets of three with similar properties.
5. In Dobereiner’s triads, the atomic mass of the middle element is
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 observation.
6. Newlands proposed the law of
A. triads
B. octaves
C. periodicity
D. atomic numbers
Answer: B
Explanation: Properties repeat after every eighth element.
7. Newlands’ law failed mainly because
A. it applied to heavy elements
B. it worked only up to calcium
C. noble gases were unknown
D. atomic masses were incorrect
Answer: B
Explanation: Beyond calcium, the law did not hold true.
8. Mendeleev arranged elements in order of increasing
A. atomic number
B. atomic volume
C. atomic mass
D. density
Answer: C
Explanation: Mendeleev’s periodic table was mass-based.
Section C: Mendeleev’s Periodic Table
9. One major achievement of Mendeleev’s table was
A. discovery of electrons
B. prediction of undiscovered elements
C. discovery of isotopes
D. explanation of atomic structure
Answer: B
Explanation: Mendeleev predicted properties of eka-elements.
10. Which element was predicted as eka-aluminium?
A. Gallium
B. Germanium
C. Scandium
D. Silicon
Answer: A
Explanation: Eka-aluminium was later discovered as gallium.
11. A major limitation of Mendeleev’s table was the
A. position of hydrogen
B. absence of noble gases
C. arrangement of metals
D. prediction of new elements
Answer: A
Explanation: Hydrogen shows similarity with both alkali metals and halogens.
12. Isotopes could not be explained by Mendeleev’s table because they have
A. different chemical properties
B. different atomic masses
C. same atomic mass
D. same valency only
Answer: B
Explanation: Isotopes have different masses but same properties.
Section D: Modern Periodic Law and Table
13. Modern periodic law was given by
A. Mendeleev
B. Dobereiner
C. Newlands
D. Moseley
Answer: D
Explanation: Moseley related properties to atomic number.
14. The modern periodic table contains
A. 7 periods and 16 groups
B. 16 periods and 7 groups
C. 7 periods and 18 groups
D. 18 periods and 7 groups
Answer: C
Explanation: The modern table has 7 horizontal periods and 18 vertical groups.
15. Elements of the same group have
A. same atomic size
B. same number of shells
C. same valence electrons
D. same atomic mass
Answer: C
Explanation: Valence electrons determine chemical similarity.
16. Period number indicates the number of
A. electrons
B. protons
C. valence electrons
D. shells
Answer: D
Explanation: Period number equals the number of occupied shells.
Section E: Electronic Configuration and Periodicity
17. Which block of elements has the general configuration ns¹?
A. p-block
B. d-block
C. s-block
D. f-block
Answer: C
Explanation: Alkali metals belong to s-block with ns¹ configuration.
18. The element with configuration [Ne] 3s² 3p⁵ belongs to
A. group 16
B. group 17
C. group 18
D. group 15
Answer: B
Explanation: Seven valence electrons place it in group 17 (halogens).
19. Noble gases have completely filled
A. s-orbitals
B. p-orbitals
C. valence shells
D. d-orbitals
Answer: C
Explanation: Their filled valence shells make them inert.
Section F: Periodic Trends – Atomic Radius
20. Atomic radius decreases across a period due to
A. increase in shells
B. increase in nuclear charge
C. shielding effect
D. increase in atomic mass
Answer: B
Explanation: Greater nuclear charge pulls electrons closer.
21. Atomic radius increases down a group because of
A. increased nuclear charge
B. decreased electrons
C. addition of new shells
D. increased electronegativity
Answer: C
Explanation: Extra shells increase atomic size.
22. Which element has the largest atomic radius?
A. Lithium
B. Sodium
C. Potassium
D. Cesium
Answer: D
Explanation: Atomic radius increases down the group.
Section G: Ionisation Enthalpy
23. Ionisation enthalpy is the energy required to
A. add an electron
B. remove an electron
C. break a bond
D. form an ion
Answer: B
Explanation: It refers to removal of the outermost electron.
24. Ionisation enthalpy generally
A. increases down a group
B. decreases across a period
C. decreases down a group
D. remains constant
Answer: C
Explanation: Increased size makes electron removal easier.
25. Which element has the highest ionisation enthalpy?
A. Sodium
B. Magnesium
C. Chlorine
D. Neon
Answer: D
Explanation: Noble gases have maximum ionisation enthalpy.
Section H: Electron Gain Enthalpy
26. Electron gain enthalpy is associated with
A. loss of electron
B. gain of electron
C. sharing of electrons
D. bonding
Answer: B
Explanation: It measures energy change when an electron is added.
27. Halogens have highly negative electron gain enthalpy because they
A. have large size
B. have stable noble gas configuration on gaining electron
C. lose electrons easily
D. have low electronegativity
Answer: B
Explanation: They readily gain one electron.
28. Which element has the most negative electron gain enthalpy?
A. Oxygen
B. Fluorine
C. Chlorine
D. Nitrogen
Answer: C
Explanation: Chlorine releases maximum energy on gaining electron.
Section I: Electronegativity
29. Electronegativity is the tendency of an atom to
A. lose electrons
B. gain protons
C. attract electrons
D. donate neutrons
Answer: C
Explanation: It measures electron-attracting ability in a bond.
30. Electronegativity increases
A. down a group
B. across a period
C. randomly
D. with atomic mass
Answer: B
Explanation: Increasing nuclear charge attracts electrons more strongly.
31. The most electronegative element is
A. Oxygen
B. Nitrogen
C. Chlorine
D. Fluorine
Answer: D
Explanation: Fluorine has the highest electronegativity.
Section J: Valency and Chemical Reactivity
32. Valency of an element depends on
A. atomic mass
B. atomic number
C. valence electrons
D. number of neutrons
Answer: C
Explanation: Valency is related to electrons in the outermost shell.
33. Alkali metals are highly reactive because they
A. have high electronegativity
B. easily lose one electron
C. have small atomic size
D. have high ionisation energy
Answer: B
Explanation: Loss of one electron gives stable noble gas configuration.
34. Halogens are highly reactive because they
A. lose electrons easily
B. gain electrons easily
C. are metals
D. have low electron affinity
Answer: B
Explanation: They readily gain one electron.
Section K: Metallic and Non-Metallic Character
35. Metallic character increases
A. across a period
B. down a group
C. with electronegativity
D. with ionisation energy
Answer: B
Explanation: Larger size makes electron loss easier.
36. Non-metallic character increases
A. down a group
B. with atomic size
C. across a period
D. with shielding effect
Answer: C
Explanation: Smaller size and higher electronegativity favour non-metals.
37. Which element shows maximum metallic character?
A. Lithium
B. Sodium
C. Potassium
D. Cesium
Answer: D
Explanation: Cesium is the most electropositive.
Section L: Anomalies and Special Trends
38. First element of each group shows anomalous behaviour due to
A. large size
B. absence of d-orbitals
C. high electronegativity
D. low atomic mass only
Answer: B
Explanation: Small size and no d-orbitals cause anomalies.
39. Diagonal relationship is observed between
A. Li and Be
B. Li and Mg
C. Be and B
D. Na and K
Answer: B
Explanation: Li and Mg show similar properties.
Section M: Conceptual NCERT-Based MCQs
40. Periodicity in properties is due to periodic repetition of
A. atomic mass
B. atomic size
C. valence shell configuration
D. nuclear mass
Answer: C
Explanation: Similar valence configuration causes similar properties.
41. Shielding effect increases
A. across a period
B. down a group
C. randomly
D. with electronegativity
Answer: B
Explanation: More inner shells increase shielding.
42. Which block elements show maximum variation in oxidation states?
A. s-block
B. p-block
C. d-block
D. f-block
Answer: C
Explanation: Transition elements show variable oxidation states.
Section N: Final High-Order MCQs
43. The most reactive non-metal is
A. Oxygen
B. Nitrogen
C. Chlorine
D. Fluorine
Answer: D
Explanation: Fluorine’s high electronegativity makes it most reactive.
44. The least reactive elements belong to
A. alkali metals
B. halogens
C. noble gases
D. alkaline earth metals
Answer: C
Explanation: Completely filled valence shells make them inert.
45. Which property shows irregular trend across a period?
A. Atomic radius
B. Electronegativity
C. Ionisation enthalpy
D. Electron gain enthalpy
Answer: D
Explanation: Electron gain enthalpy shows exceptions.
46. s-Block elements are mostly
A. non-metals
B. metalloids
C. metals
D. noble gases
Answer: C
Explanation: s-Block elements are highly electropositive metals.
47. p-Block elements include
A. only metals
B. only non-metals
C. metals, non-metals and metalloids
D. noble gases only
Answer: C
Explanation: p-Block shows maximum diversity.
48. Which property helps in predicting chemical behaviour?
A. atomic mass
B. valence electrons
C. atomic volume
D. density
Answer: B
Explanation: Chemical behaviour depends on valence electrons.
49. Periodic classification mainly helps in
A. discovering new isotopes
B. predicting properties of elements
C. explaining nuclear reactions
D. studying radioactivity
Answer: B
Explanation: Periodicity allows prediction of properties.
50. The modern periodic table is the result of
A. one scientist’s work
B. trial and error
C. contributions of many scientists
D. accidental discovery
Answer: C
Explanation: It evolved through contributions of many scientists.
✅ Completion Note
This completes a fully NCERT-aligned, CBSE-standard set of 50 MCQs on Classification of Elements and Periodicity, ideal for concept clarity, systematic revision, and board exam preparation.