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Periodic Table &
Classification of Elements
A comprehensive, exam-ready practice platform featuring every question type — from MCQs to HOTS, case-based to application questions. Answers hidden until revealed.
Mendeleev’s Periodic Law
Modern Periodic Law
Electronic Configuration
s, p, d, f Blocks
Metals & Non-Metals
Atomic Size & Electronegativity
Electropositivity & Valency
Reactivity of Elements
🎯 Multiple Choice Questions
30 carefully crafted MCQs covering all topics. Click an option to check your answer. Track your score on the scoreboard.
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Mendeleev arranged elements in his periodic table in order of their increasing:
❌ Incorrect. Mendeleev used atomic mass as the basis for arranging elements (Option B is correct).
✅ Correct! Mendeleev’s Periodic Law states that properties of elements are a periodic function of their atomic masses.
The Modern Periodic Law was proposed by:
✅ Correct! Henry Moseley (1913) discovered that atomic number, not atomic mass, is the fundamental property.
❌ Incorrect. Henry Moseley proposed the Modern Periodic Law based on atomic numbers.
The electronic configuration of Sodium (Na, Z=11) is:
✅ Correct! Na(11): 1s²2s²2p⁶3s¹ → shell notation: 2, 8, 1. One valence electron in the 3s sub-shell.
❌ Incorrect. Na has 11 electrons: 2 in K, 8 in L, 1 in M shell → 2, 8, 1.
Which of the following belongs to the d-block?
✅ Correct! Iron (Fe, Z=26) is a transition metal — its last electron enters the 3d sub-shell (d-block).
❌ Incorrect. Iron (Fe) is the d-block element. Ca is s-block, Cl is p-block, Ne is p-block.
Atomic radius generally __________ across a period from left to right.
✅ Correct! Across a period, nuclear charge increases while electrons are added to the same shell, pulling them closer → atomic radius decreases.
❌ Incorrect. Atomic radius decreases left to right across a period due to increasing nuclear charge.
The most electronegative element in the periodic table is:
✅ Correct! Fluorine (F) has the highest electronegativity value of 4.0 on the Pauling scale.
❌ Incorrect. Fluorine is the most electronegative element (Pauling scale: 4.0).
The number of groups in the modern periodic table is:
✅ Correct! The Modern Periodic Table has 18 groups and 7 periods.
❌ Incorrect. The Modern Periodic Table has 18 groups and 7 periods.
Which element has electronic configuration 1s²2s²2p⁶3s²3p⁶4s²?
✅ Correct! Calcium (Ca, Z=20): 1s²2s²2p⁶3s²3p⁶4s² — last electrons enter 4s, making it an s-block element.
❌ Incorrect. This is Calcium (Ca, Z=20) — count: 2+2+6+2+6+2 = 20 electrons.
Silicon (Si) is classified as a:
✅ Correct! Silicon (Si) is a metalloid/semimetal — it shows properties of both metals and non-metals. Used in semiconductors!
❌ Incorrect. Silicon is a metalloid (semimetal). It lies along the staircase line in the periodic table.
The valency of an element with electronic configuration 2, 8, 7 is:
✅ Correct! With 7 valence electrons, the element needs 1 more to complete the octet → Valency = 1 (e.g., Chlorine).
❌ Incorrect. 7 valence electrons → needs 1 electron to complete octet → Valency = 1.
Which block contains the noble gases?
✅ Correct! Noble gases (Group 18) are p-block elements — their outermost electrons fill the p sub-shell (ns²np⁶ configuration).
❌ Incorrect. Noble gases belong to p-block (Group 18, configuration ns²np⁶).
The period number of an element corresponds to:
✅ Correct! Period number = highest principal quantum number (n) of the element’s electronic configuration.
❌ Incorrect. Period number = highest principal quantum number (n) in the element’s configuration.
Electropositivity (metallic character) increases as you move:
✅ Correct! Down a group, atomic size increases, electrons are farther from nucleus — easier to lose electrons → electropositivity increases.
❌ Incorrect. Electropositivity (metallic character) increases down a group.
The most electropositive (most reactive metal) in the periodic table is:
✅ Correct! Caesium (Cs) — at the bottom-left of the periodic table — is the most electropositive metal (excluding radioactive Fr).
❌ Incorrect. Caesium (Cs) is the most electropositive element (excluding radioactive francium).
The f-block elements are also called:
✅ Correct! f-block elements include Lanthanoids (57-71) and Actinoids (89-103), collectively called inner transition elements.
❌ Incorrect. f-block = Inner transition elements (Lanthanoids and Actinoids).
Phosphorus (P, Z=15) electronic sub-shell configuration is:
✅ Correct! P(15): 1s²2s²2p⁶3s²3p³ → 2+2+6+2+3 = 15 electrons. 3 unpaired electrons → valency 3.
❌ Incorrect. P(15) = 1s²2s²2p⁶3s²3p³. Count: 2+2+6+2+3 = 15 ✓
Which of the following is a metalloid?
✅ Correct! Arsenic (As) is a metalloid, positioned along the diagonal staircase in the periodic table.
❌ Incorrect. Arsenic (As) is a metalloid. Metalloids: B, Si, Ge, As, Sb, Te, Po.
Mendeleev left gaps in his periodic table. These gaps were later filled by:
✅ Correct! Mendeleev predicted Eka-boron (Sc), Eka-aluminium (Ga), Eka-silicon (Ge) — all later discovered and filled his gaps.
❌ Incorrect. Gaps were filled by newly discovered elements (Ga, Sc, Ge) that Mendeleev had predicted.
In the modern periodic table, the group number of an s-block element with 2 valence electrons is:
✅ Correct! s-block with 2 valence electrons = ns² configuration → Group 2 (alkaline earth metals).
❌ Incorrect. 2 valence electrons in s sub-shell (ns²) = Group 2 (alkaline earth metals).
Reactivity of non-metals generally __________ down the group.
✅ Correct! Non-metal reactivity decreases down a group — larger atoms have weaker electron affinity, making them less reactive.
❌ Incorrect. Non-metal reactivity decreases down a group (opposite of metals).
The element with configuration [He] 2s² is placed in which period and group?
✅ Correct! [He]2s² = Beryllium (Be, Z=4). Highest n=2 → Period 2. Two valence electrons in s → Group 2.
❌ Incorrect. [He]2s² is Be (Z=4) → Period 2, Group 2 (n=2 → period 2; 2 valence e⁻ → Group 2).
Mendeleev’s periodic law failed to explain the position of:
✅ Correct! Isotopes have the same atomic number but different atomic masses. Mendeleev’s mass-based law couldn’t place isotopes in different positions — they’d occupy one spot.
❌ Incorrect. Isotopes were a major anomaly — Mendeleev’s law based on mass couldn’t properly account for them.
Elements in the same group of the periodic table have the same:
✅ Correct! All elements in a group share the same number of valence electrons, giving them similar chemical properties.
❌ Incorrect. Same group → same number of valence electrons → similar chemical properties.
The element Argon (Ar, Z=18) has electronic configuration:
✅ Correct! Ar(18): K=2, L=8, M=8 → 2,8,8. It’s a noble gas with stable full outer shell.
❌ Incorrect. Ar(18) = 2, 8, 8. K shell fills with 2, L with 8, M with 8.
Which of the following correctly defines electronegativity?
✅ Correct! Electronegativity = tendency of an atom to attract the shared pair of electrons in a covalent bond towards itself (Pauling scale).
❌ Incorrect. Electronegativity = tendency to attract shared electrons in a bond. Electron affinity = energy released when e⁻ added.
Which group in the modern periodic table contains the alkali metals?
✅ Correct! Group 1 = Alkali metals (Li, Na, K, Rb, Cs, Fr). They have one valence electron and are highly reactive.
❌ Incorrect. Alkali metals are in Group 1 (ns¹ configuration).
The element with highest atomic number in Period 3 is:
✅ Correct! Period 3 runs from Na (Z=11) to Ar (Z=18). Argon with Z=18 is the last element of Period 3.
❌ Incorrect. Period 3: Na(11) to Ar(18). Argon (Ar, Z=18) is last.
Which of the following elements shows variable valency?
✅ Correct! Iron (Fe) shows variable valency — Fe²⁺ (ferrous) and Fe³⁺ (ferric) — due to partially filled d orbitals in transition metals.
❌ Incorrect. Iron (Fe) shows variable valency (2 and 3) because of its partially filled 3d orbitals.
The s-block comprises Groups:
✅ Correct! s-block = Groups 1 & 2. Their distinguishing electrons enter the s sub-shell (ns¹ or ns² configuration).
❌ Incorrect. s-block = Groups 1 and 2. d-block = Groups 3–12. p-block = Groups 13–18.
An element has electronic configuration 2, 8, 8, 2. It belongs to which period and block?
✅ Correct! 2+8+8+2 = 20 electrons → Calcium (Ca, Z=20). Config: 1s²2s²2p⁶3s²3p⁶4s² → highest n=4 → Period 4. Last e⁻ in 4s → s-block.
❌ Incorrect. Z=20 = Ca. Config ends in 4s² → Period 4, s-block.
✔ True / False Questions
Click the answer button to reveal whether the statement is True or False, along with an explanation.
TF 01
Mendeleev arranged elements in increasing order of atomic number.
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🔴 FALSE
Mendeleev arranged elements in increasing order of atomic mass, not atomic number. It was Moseley who later showed that atomic number (not mass) is the fundamental property.
TF 02
Modern Periodic Law states that properties of elements are a periodic function of their atomic numbers.
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🟢 TRUE
This is the exact statement of Modern Periodic Law, proposed by Moseley (1913). The arrangement by atomic number resolves anomalies in Mendeleev’s table.
TF 03
Electronegativity increases down a group.
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🔴 FALSE
Electronegativity decreases down a group. As atomic size increases, the nucleus is farther from the bonding electrons, reducing its ability to attract them.
TF 04
The electronic configuration of Potassium (K, Z=19) is 2, 8, 9.
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🔴 FALSE
K(19) configuration is 2, 8, 8, 1 (or 1s²2s²2p⁶3s²3p⁶4s¹). The 19th electron goes into the 4s sub-shell, not the 3rd shell, because 4s is at a lower energy than 3d.
TF 05
Atomic radius increases across a period from left to right.
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🔴 FALSE
Atomic radius decreases left to right across a period. Increased nuclear charge (proton count) pulls electrons closer without adding new shells.
TF 06
d-block elements are also called transition elements.
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🟢 TRUE
d-block elements (Groups 3–12) are called transition elements because they are intermediate (transition) between the highly electropositive s-block metals and the p-block elements.
TF 07
Halogens are the most reactive non-metals.
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🟢 TRUE
Halogens (Group 17) are the most reactive non-metals. They need just one electron to complete their octet, giving them the highest electron affinity among non-metals.
TF 08
Metalloids have properties intermediate between metals and non-metals.
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🟢 TRUE
Metalloids (B, Si, Ge, As, Sb, Te, Po) exhibit intermediate properties. For example, Silicon looks metallic (shiny) but is a semiconductor — neither a good conductor nor a perfect insulator.
TF 09
The modern periodic table has 7 periods and 18 groups.
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🟢 TRUE
The Modern Periodic Table has exactly 7 horizontal periods and 18 vertical groups (columns).
TF 10
Reactivity of alkali metals increases down the group.
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🟢 TRUE
Down Group 1, atomic size increases, and the outermost electron is held less tightly, making it easier to lose → reactivity increases. Cs > Rb > K > Na > Li.
✏️ Fill in the Blanks
Read the statement and click “Reveal Answer” to see the missing word(s).
🔗 Match the Following
Match Column A with Column B. Click “Show Answers” to verify.
📝 Short Answer Questions
30 short answer questions — click any question to reveal the model answer.
📚 Long Answer / Descriptive Questions
Detailed questions requiring elaborate answers. Click to reveal full model answer.
🧠 Higher Order Thinking Skills (HOTS)
Application, analysis, and evaluation-level questions that test deep understanding.
⚖️ Assertion & Reason Questions
Select the correct option for each Assertion-Reason pair.
📋 Case-Based Questions
Read each case/scenario and answer the questions that follow.
🗺 Diagram & Labeling Questions
Interpret diagrams, label elements, and answer diagram-based questions.
🎮 Knowledge Games
Learn while playing! Test your knowledge with interactive games.
Element Flashcards
Flip cards to match elements with their properties, positions, and configurations.
Quick Fire Quiz
Race against time! 10 rapid questions about periodic trends. How many can you get right?
Config Builder
Given an atomic number (1-20), identify its full electronic configuration — sub-shell style!
Block Sorter
Classify given elements into s, p, d, or f blocks as fast as possible.
🃏 Element Flashcards
Click the card to flip it and see the answer!
👆 Click card to reveal • Then mark yourself
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🔢 Config Builder
Select the correct full electronic configuration for the element shown.
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🧩 Block Sorter
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💡 Key Concepts at a Glance
Quick conceptual references for all major topics in this chapter.
Mendeleev’s Periodic Law
Properties of elements are a periodic function of their atomic masses. Predicted missing elements (Eka-Al, Eka-Si) and left gaps for them.
Modern Periodic Law
Properties are a periodic function of atomic number (Moseley, 1913). Resolves all anomalies of Mendeleev’s table.
Aufbau Principle
Electrons fill orbitals in order of increasing energy: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p…
Atomic Size Trend
↓ Decreases across a period (↑ nuclear charge). ↑ Increases down a group (new shells added).
Electronegativity
Ability to attract bonding electrons. Highest: F (4.0). Increases across period; decreases down group (Pauling scale).
Electropositivity
Tendency to lose electrons. Opposite of electronegativity. Increases down group; decreases across period.
Valency
Combining capacity = electrons needed to complete octet. For non-metals: 8 − valence e⁻. For metals: valence e⁻.
Block Classification
s-block: Gr 1–2 | p-block: Gr 13–18 | d-block: Gr 3–12 | f-block: Lanthanoids & Actinoids.
Reactivity Trends
Metals: reactivity ↑ down group. Non-metals: reactivity ↓ down group. Most reactive metal: Cs. Most reactive non-metal: F.
Metalloid Position
Along the staircase (zigzag) line: B, Si, Ge, As, Sb, Te, Po. Show properties of both metals and non-metals.
Period vs Group
Period = row (same highest n). Group = column (same valence electrons, similar chemistry).
Noble Gases
Group 18, p-block (ns²np⁶). Completely filled outer shell → chemically inert. He: 1s²; Others: ns²np⁶.
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