MCQs on p-Block Elements – CBSE Class 12 Chemistry
MCQs on p-Block Elements – CBSE Class 12 Chemistry
Inorganic Chemistry | NCERT-Based | MCQs with Answers & Explanations
The following 50 Multiple Choice Questions (MCQs) are strictly aligned with the NCERT syllabus for CBSE Class 12 Chemistry.
Questions are arranged section-wise (Group 13 to Group 18) with concept-clearing explanations, making them ideal for board exam preparation.
Section A: Group 13 Elements (Boron Family)
Q1. Which element of Group 13 shows anomalous behavior?
A. Aluminium
B. Gallium
C. Boron
D. Indium
Answer: C
Explanation:
Boron shows anomalous behavior due to its small size, high ionization enthalpy, and absence of d-orbitals, unlike other members.
Q2. The most stable oxidation state of aluminium is:
A. +1
B. +2
C. +3
D. +5
Answer: C
Explanation:
Aluminium predominantly exhibits the +3 oxidation state due to loss of three valence electrons.
Q3. Which compound of boron acts as a Lewis acid?
A. B₂H₆
B. BF₃
C. B₂O₃
D. Borax
Answer: B
Explanation:
BF₃ has an electron-deficient boron atom, making it a strong Lewis acid.
Q4. Which metal is used as a catalyst in the Haber process when promoted with K₂O?
A. Aluminium
B. Boron
C. Iron
D. Gallium
Answer: C
Explanation:
Iron is the main catalyst; promoters like K₂O increase its efficiency.
Q5. The hybridisation of boron in BF₃ is:
A. sp
B. sp²
C. sp³
D. dsp²
Answer: B
Explanation:
Boron forms three sigma bonds in BF₃, giving trigonal planar geometry with sp² hybridisation.
Section B: Group 14 Elements (Carbon Family)
Q6. The most stable allotrope of carbon under normal conditions is:
A. Graphite
B. Diamond
C. Fullerene
D. Charcoal
Answer: A
Explanation:
Graphite is thermodynamically more stable due to delocalized π-electrons.
Q7. Which element shows maximum catenation?
A. Silicon
B. Carbon
C. Tin
D. Lead
Answer: B
Explanation:
Carbon forms strong C–C bonds, leading to maximum catenation.
Q8. CO is poisonous because it:
A. Reacts with oxygen
B. Reduces haemoglobin
C. Forms carboxyhaemoglobin
D. Causes lung irritation
Answer: C
Explanation:
CO binds haemoglobin irreversibly to form carboxyhaemoglobin, blocking oxygen transport.
Q9. The oxidation state of carbon in CO₂ is:
A. +2
B. +4
C. −4
D. 0
Answer: B
Explanation:
Each oxygen is −2, so carbon must be +4.
Q10. Which compound shows linear geometry?
A. CH₄
B. CO₂
C. NH₃
D. H₂O
Answer: B
Explanation:
CO₂ has sp hybridisation, resulting in a linear structure.
Section C: Group 15 Elements (Nitrogen Family)
Q11. Nitrogen shows anomalous behavior due to:
A. High atomic mass
B. Low electronegativity
C. Small size and high electronegativity
D. Presence of d-orbitals
Answer: C
Explanation:
Small size and strong N≡N bond cause anomalous properties.
Q12. Which oxide of nitrogen is neutral?
A. N₂O
B. NO₂
C. N₂O₅
D. NO
Answer: A
Explanation:
N₂O is a neutral oxide.
Q13. The hybridisation of nitrogen in NH₃ is:
A. sp
B. sp²
C. sp³
D. dsp²
Answer: C
Explanation:
NH₃ has three bond pairs and one lone pair → sp³ hybridisation.
Q14. Which nitrogen oxide is paramagnetic?
A. N₂O
B. NO
C. N₂O₅
D. N₂O₃
Answer: B
Explanation:
NO has one unpaired electron, making it paramagnetic.
Q15. White phosphorus is stored under water because it:
A. Is toxic
B. Is volatile
C. Reacts with air
D. Is soft
Answer: C
Explanation:
White phosphorus oxidizes spontaneously in air.
Section D: Group 16 Elements (Oxygen Family)
Q16. The most electronegative element in Group 16 is:
A. Sulphur
B. Oxygen
C. Selenium
D. Tellurium
Answer: B
Explanation:
Oxygen has the smallest size and highest electronegativity.
Q17. Which allotrope of oxygen is diamagnetic?
A. O₂
B. O₃
C. Atomic oxygen
D. Nascent oxygen
Answer: B
Explanation:
Ozone (O₃) has no unpaired electrons, hence diamagnetic.
Q18. SO₂ acts as a:
A. Oxidizing agent only
B. Reducing agent only
C. Both oxidizing and reducing agent
D. Neutral gas
Answer: C
Explanation:
SO₂ can both gain and lose electrons, showing dual behavior.
Q19. The oxidation state of sulphur in H₂SO₄ is:
A. +4
B. +6
C. −2
D. 0
Answer: B
Explanation:
Sulphur exhibits +6 oxidation state in sulphuric acid.
Q20. Which acid is called the “King of Chemicals”?
A. HNO₃
B. HCl
C. H₂SO₄
D. H₃PO₄
Answer: C
Explanation:
Sulphuric acid is widely used in industries, hence called the King of Chemicals.
Section E: Group 17 Elements (Halogens)
Q21. The most electronegative element is:
A. Chlorine
B. Bromine
C. Fluorine
D. Iodine
Answer: C
Explanation:
Fluorine has the highest electronegativity due to its small size.
Q22. Which halogen shows only −1 oxidation state?
A. Chlorine
B. Bromine
C. Iodine
D. Fluorine
Answer: D
Explanation:
Fluorine cannot expand its octet and shows only −1 state.
Q23. The strongest oxidizing agent among halogens is:
A. I₂
B. Br₂
C. Cl₂
D. F₂
Answer: D
Explanation:
Fluorine has the highest reduction potential.
Q24. Which acid is strongest?
A. HF
B. HCl
C. HBr
D. HI
Answer: D
Explanation:
Bond strength decreases down the group, so HI ionizes most easily.
Q25. Which compound is used as bleaching powder?
A. CaCl₂
B. Ca(OCl)Cl
C. NaClO
D. Cl₂
Answer: B
Explanation:
Bleaching powder is calcium oxychloride, Ca(OCl)Cl.
Section F: Group 18 Elements (Noble Gases)
Q26. Noble gases are also called inert gases because they:
A. Are heavy
B. Are colorless
C. Have stable electronic configuration
D. Do not exist freely
Answer: C
Explanation:
Their completely filled valence shells make them chemically inert.
Q27. Which noble gas forms the maximum number of compounds?
A. Helium
B. Neon
C. Argon
D. Xenon
Answer: D
Explanation:
Xenon has lower ionization energy and available d-orbitals.
Q28. Which compound has xenon in +6 oxidation state?
A. XeF₂
B. XeF₄
C. XeF₆
D. XeO₃
Answer: C
Explanation:
In XeF₆, xenon shows +6 oxidation state.
Q29. The shape of XeF₄ molecule is:
A. Tetrahedral
B. Square planar
C. Trigonal bipyramidal
D. Octahedral
Answer: B
Explanation:
XeF₄ has square planar geometry due to two lone pairs.
Q30. Noble gases are monoatomic because:
A. They are light
B. They are gases
C. They have zero valency
D. They are radioactive
Answer: C
Explanation:
Complete octet makes them chemically unreactive.
Section G: Mixed Conceptual & NCERT-Based MCQs
Q31. Which p-block element is liquid at room temperature?
A. Bromine
B. Iodine
C. Mercury
D. Gallium
Answer: A
Explanation:
Bromine is the only liquid non-metal at room temperature.
Q32. Down the group, metallic character:
A. Decreases
B. Remains same
C. Increases
D. First increases then decreases
Answer: C
Explanation:
Atomic size increases down the group, enhancing metallic nature.
Q33. Which oxide is amphoteric?
A. SO₂
B. Al₂O₃
C. CO₂
D. P₂O₅
Answer: B
Explanation:
Al₂O₃ reacts with both acids and bases.
Q34. Which element shows maximum oxidation state of +7?
A. Nitrogen
B. Chlorine
C. Phosphorus
D. Sulphur
Answer: B
Explanation:
Chlorine shows +7 oxidation state in perchloric acid (HClO₄).
Q35. Which p-block element is used in semiconductor devices?
A. Aluminium
B. Boron
C. Silicon
D. Phosphorus
Answer: C
Explanation:
Silicon is widely used due to its semiconducting properties.
Q36. Which hydride is most stable?
A. NH₃
B. PH₃
C. AsH₃
D. SbH₃
Answer: A
Explanation:
Stability decreases down the group due to weaker E–H bonds.
Q37. The bond angle in NH₃ is less than tetrahedral because of:
A. Bond pair–bond pair repulsion
B. Lone pair–bond pair repulsion
C. Lone pair–lone pair repulsion
D. Hydrogen bonding
Answer: B
Explanation:
Lone pair–bond pair repulsion reduces the bond angle.
Q38. Which gas is responsible for acid rain?
A. CO₂
B. SO₂
C. NO
D. N₂O
Answer: B
Explanation:
SO₂ forms sulphuric acid in the atmosphere.
Q39. Which halogen is radioactive?
A. Fluorine
B. Chlorine
C. Bromine
D. Astatine
Answer: D
Explanation:
Astatine is naturally radioactive.
Q40. Which noble gas is used in filling electric bulbs?
A. Neon
B. Argon
C. Krypton
D. Xenon
Answer: B
Explanation:
Argon prevents oxidation of tungsten filament.
Q41. The acidic character of oxides increases:
A. Down the group
B. Across the period
C. Randomly
D. With metallic nature
Answer: B
Explanation:
Non-metallic character increases across a period, increasing acidity.
Q42. Which p-block element shows allotropy?
A. Boron
B. Carbon
C. Nitrogen
D. Fluorine
Answer: B
Explanation:
Carbon shows diamond, graphite, and fullerene forms.
Q43. Which oxide of nitrogen is used as laughing gas?
A. NO
B. N₂O
C. NO₂
D. N₂O₅
Answer: B
Explanation:
N₂O causes mild anesthesia, hence called laughing gas.
Q44. The strongest reducing agent among halide ions is:
A. F⁻
B. Cl⁻
C. Br⁻
D. I⁻
Answer: D
Explanation:
Reducing power increases down the group.
Q45. Which p-block element forms electron-deficient compounds?
A. Carbon
B. Boron
C. Nitrogen
D. Oxygen
Answer: B
Explanation:
Boron compounds like BF₃ have incomplete octets.
Q46. The noble gas with highest atomic radius is:
A. Argon
B. Krypton
C. Xenon
D. Radon
Answer: D
Explanation:
Atomic size increases down the group.
Q47. Which compound acts as a dehydrating agent?
A. HNO₃
B. H₂SO₄
C. HCl
D. H₃PO₄
Answer: B
Explanation:
Concentrated sulphuric acid removes water effectively.
Q48. Which halogen has the highest bond dissociation energy?
A. F₂
B. Cl₂
C. Br₂
D. I₂
Answer: B
Explanation:
Cl–Cl bond is strongest due to optimal atomic size.
Q49. Which oxide is basic in nature?
A. CO₂
B. SO₂
C. N₂O₅
D. Al₂O₃
Answer: D
Explanation:
Al₂O₃ shows basic behavior with acids.
Q50. Which noble gas is used in advertising signboards?
A. Helium
B. Neon
C. Argon
D. Xenon
Answer: B
Explanation:
Neon emits bright red-orange light in discharge tubes.
✅ Exam Ready Tip:
These MCQs are NCERT-faithful, concept-driven, and perfect for CBSE board revision, assertion–reason prep, and competitive exam fundamentals.