Key Fact
Blocks of periodic table
s-block (groups 1, 2): outermost s; p-block (groups 13-18): outermost p; d-block (groups 3-12): incomplete d; f-block (lanthanides, actinides): incomplete f.
-- NCERT Class 11 Chemistry, Ch. 3, p. 82Blocks of Periodic Table
8 MCQs9-step worked example
Source: NCERT Classification of Elements and Periodicity in PropertiesPYQ coverage: NEET 2025Official key: NTA-verifiedLast updated: 26 Sep 2026
Blocks of Periodic Table, explained for NEET
The modern periodic table groups 118 elements into four blocks — s, p, d, and f — named after the subshell that receives the last electron in the ground-state electronic configuration. This classification is the backbone of inorganic chemistry for NEET: once you know the block, you can predict valence, bonding behaviour, and broad chemical trends.
s-block (Groups 1 and 2): The differentiating electron enters the outermost s-orbital. Group 1 elements (alkali metals: Li to Fr) have the configuration ns¹; Group 2 elements (alkaline earth metals: Be to Ba) have ns². Hydrogen and helium technically belong to the s-block by configuration (1s¹ and 1s²), though helium is placed with noble gases due to its filled-shell chemistry (NCERT Class 11 Chemistry Chapter 3, page 82).
p-block (Groups 13–18): The differentiating electron enters the outermost p-orbital (ns²np¹ to ns²np⁶). This block includes metals, metalloids, and non-metals — the widest chemical diversity. Noble gases (Group 18) complete the block with ns²np⁶ (except He: 1s²).
d-block (Groups 3–12): The differentiating electron enters the (n−1)d orbital. General outer configuration: (n−1)d¹⁻¹⁰ ns⁰⁻². These are the transition metals (though Zn, Cd, Hg with d¹⁰ are debated — NEET treats Groups 3–12 as d-block).
f-block (Lanthanoids and Actinoids): The differentiating electron enters the (n−2)f orbital. Lanthanoids: 4f¹⁻¹⁴ 5d⁰⁻¹ 6s². Actinoids: 5f¹⁻¹⁴ 6d⁰⁻¹ 7s². These two rows sit below the main table.
Watch-out for NEET: The question "Which block does element X belong to?" tests one thing — which subshell receives the last electron. Don't confuse the block label with the outermost shell. For d-block, the differentiating electron is in (n−1)d, not ns. For f-block, it is (n−2)f. Getting the "differentiating electron" definition wrong is a common source of lost marks.
Can you answer these Blocks of Periodic Table MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
The elements in which the last electron enters the outermost s-orbital belong to which block of the periodic table?
Show answer and why every option is right or wrong
Answer: B. By definition, elements whose differentiating (last) electron enters the outermost s-orbital are classified as s-block elements (NCERT Class 11 Chemistry Chapter 3, page 82).
Why A is wrong: A is wrong because p-block elements have their last electron entering the outermost p-orbital, not s-orbital.
Why C is wrong: C is wrong because d-block elements have their last electron entering the (n−1)d subshell.
Why D is wrong: D is wrong because f-block elements have their last electron entering the (n−2)f subshell.
MCQ 2Easy RecallPractice
Which of the following groups constitute the s-block of the periodic table?
Show answer and why every option is right or wrong
Answer: D. Groups 1 (alkali metals) and 2 (alkaline earth metals) form the s-block, where the differentiating electron enters the ns-orbital (NCERT Class 11 Chemistry Chapter 3, page 82).
Why A is wrong: A is wrong because Groups 3–12 constitute the d-block, where the differentiating electron enters the (n−1)d subshell.
Why B is wrong: B is wrong because Groups 13–18 constitute the p-block, where the differentiating electron enters the np subshell.
Why C is wrong: C is wrong because lanthanoids and actinoids constitute the f-block, where the differentiating electron enters the (n−2)f subshell.
MCQ 3Easy RecallPractice
Helium (He) has the electronic configuration 1s². Strictly by its differentiating electron it belongs to the s-block. In which block is it actually POSITIONED in the periodic table?
Show answer and why every option is right or wrong
Answer: A. Although helium's configuration (1s²) resembles s-block, it is placed in Group 18 (p-block) with noble gases because of its completely filled valence shell and inert chemical behaviour (NCERT Class 11 Chemistry Chapter 3, page 82).
Why B is wrong: B is wrong because while helium's electronic configuration is ns², its chemistry (completely filled shell, inertness) aligns with noble gases, not alkaline earth metals. NCERT places it in Group 18.
Why C is wrong: C is wrong because d-block requires a differentiating electron in the (n−1)d subshell. Helium has no d-electrons.
Why D is wrong: D is wrong because every element is placed in the periodic table. Helium is placed in Group 18, p-block.
MCQ 4Direct ApplicationPractice
An element has the ground-state electronic configuration [Ar] 3d⁶ 4s². To which block does it belong?
Show answer and why every option is right or wrong
Answer: A. The differentiating (last-filled) electron enters the 3d subshell, making this a d-block element. The element is iron (Fe), Group 8 (NCERT Class 11 Chemistry Chapter 3, page 84).
Why B is wrong: B is wrong because there are no p-electrons beyond the argon core in this configuration. The differentiating electron is in 3d.
Why C is wrong: C is wrong because s-block classification requires the last electron to enter the outermost s-orbital. Here the 4s was filled before 3d; the differentiating electron is in 3d, not 4s.
Why D is wrong: D is wrong because f-block requires the differentiating electron in a (n−2)f subshell. This element has no f-electrons.
MCQ 5Direct ApplicationPractice
An element has the ground-state configuration [Xe] 4f¹ 5d¹ 6s². The differentiating electron enters which subshell, and to which block does the element belong?
Show answer and why every option is right or wrong
Answer: B. The differentiating electron enters the 4f subshell (the (n−2)f orbital relative to the outermost shell n = 6). This makes the element an f-block (lanthanoid) element — specifically cerium (Ce, Z = 58); lanthanum is [Xe] 5d¹ 6s², with no 4f electron. NCERT classifies elements with differentiating electron in 4f as f-block (NCERT Class 11 Chemistry Chapter 3, page 84).
Why A is wrong: A is wrong because although 6s² is present, the differentiating electron is the one that distinguishes this element from the preceding one — it enters 4f, not 6s.
Why C is wrong: C is wrong because while 5d¹ is present in the configuration, the 4f subshell is being filled across the lanthanoid series. The differentiating electron enters 4f, making it f-block, not d-block.
Why D is wrong: D is wrong because there is no 5p electron being added in this configuration. The 5p subshell is already filled within the [Xe] core.
MCQ 6Direct ApplicationPractice
Which of the following correctly represents the general outer electronic configuration of d-block elements?
Show answer and why every option is right or wrong
Answer: C. d-block elements have the differentiating electron in the (n−1)d subshell. The general outer configuration is (n−1)d¹⁻¹⁰ ns⁰⁻², where ns can be 0, 1, or 2 depending on stability considerations (NCERT Class 11 Chemistry Chapter 3, page 84).
Why A is wrong: A is wrong because ns¹⁻² np¹⁻⁶ is the general outer configuration of p-block elements (Groups 13–18).
Why B is wrong: B is wrong because ns¹⁻² alone describes the s-block elements (Groups 1 and 2) without any d-electron involvement.
Why D is wrong: D is wrong because (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns² is the general configuration of f-block elements (lanthanoids and actinoids).
MCQ 7Concept TrapPractice
A student claims that zinc (Zn, [Ar] 3d¹⁰ 4s²) should not be classified as a d-block element because its d-subshell is completely filled. Which statement best addresses this claim in the NEET context?
Show answer and why every option is right or wrong
Answer: D. While the "transition metal" label is debated for Zn/Cd/Hg (d¹⁰ configuration, no partially filled d-subshell in common oxidation states), NEET and NCERT classify all elements of Groups 3–12 as d-block elements (NCERT Class 11 Chemistry Chapter 3, page 84).
Why A is wrong: A is wrong because s-block is limited to Groups 1 and 2. Zn is in Group 12 and its differentiating electron entered the 3d subshell during the building-up process, placing it in the d-block.
Why B is wrong: B is wrong because p-block covers Groups 13–18. Zn has no differentiating p-electron.
Why C is wrong: C is wrong because f-block requires a differentiating electron in an f-subshell. Zn has no f-electrons at all. Having 10 d-electrons does not reclassify an element as f-block.
MCQ 8Concept TrapPractice
Elements of the f-block are placed separately at the bottom of the periodic table. The differentiating electron in lanthanoids enters the:
Show answer and why every option is right or wrong
Answer: C. In lanthanoids (Ce to Lu), the differentiating electron progressively fills the 4f subshell. The general configuration is [Xe] 4f¹⁻¹⁴ 5d⁰⁻¹ 6s² (NCERT Class 11 Chemistry Chapter 3, page 84).
Why A is wrong: A is wrong because the 5f subshell is filled in actinoids (Th to Lr), not lanthanoids. Confusing 4f (lanthanoids) with 5f (actinoids) is a common mix-up.
Why B is wrong: B is wrong because 3d filling characterises the first-row d-block (transition) elements (Sc to Zn), not the lanthanoids.
Why D is wrong: D is wrong because 6p filling characterises the p-block elements of period 6 (Tl to Rn). Lanthanoids fill 4f, not 6p.
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How do you solve a Blocks of Periodic Table question? A worked example
- 1
Given
Atomic number Z = 26.
- 2
Required
(a) Block classification. (b) Outer electronic configuration.
- 3
Concept
The block of an element is determined by the subshell into which the differentiating (last) electron enters during the Aufbau filling sequence.
- 4
Approach
Write the full electronic configuration using the Aufbau principle, then identify which subshell receives the final electron.
- 5
Configuration build-up
Z = 26: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²
Core: [Ar] = 1s² 2s² 2p⁶ 3s² 3p⁶
Outer: 3d⁶ 4s² - 6
Identification
The differentiating electron enters the 3d subshell (the (n−1)d orbital, where the outermost shell is n = 4). This places the element in the d-block.
The element is iron (Fe), located in Period 4, Group 8. - 7
Final answer
Element X (Z = 26) is a d-block element with outer electronic configuration [Ar] 3d⁶ 4s².
Note: Atomic number 26 is an exact counting integer and does not affect any significant-figure considerations. - 8
Common trap
Students sometimes look at the outermost shell (4s²) and classify this as s-block. The block is determined by the differentiating subshell (3d), not the outermost occupied subshell.
- 9
Similar NEET-style question
An element has atomic number 58. Identify its block and write its expected outer configuration.
*(Answer: [Xe] 4f¹ 5d¹ 6s² — f-block, lanthanoid.)*
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What to remember before solving Blocks of Periodic Table questions
More in Classification of Elements and Periodicity in Properties: 4 exam traps and mistakes · 1 formula · 1 question pattern from its other lessons.
Blocks of Periodic Table questions from past NEET papers
1 question from NEET 2025. Answers verified against NTA official keys.
NEET 2025
1A, C and D only
2B and E only
3A and C only
4D and E only
NTA Answer: Option 3(final)
All 10 past-paper questions from Classification of Elements and Periodicity in Properties →
Sources
NCERT refs: Class 11 Chemistry Chapter 3, p.82
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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