p-Block Elements (Groups 13-14)

17 NEET-UG practice questions on p-Block Elements (Groups 13-14), part of Chemistry. The first 17 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   Diborane reacts readily with water. Which products form?

   1. AB and H₂O₂
   2. BB(OH)₃ and H₂
   3. CBH₃ and O₂
   4. DB₂O₃ and H₂

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   Answer: B · B(OH)₃ and H₂

   The reaction is B₂H₆ + 6H₂O → 2B(OH)₃ + 6H₂, so boric acid and hydrogen form. Each hydrogen of B₂H₆ is released as H₂ with one hydrogen from water.

   • A: Boron is not set free and H₂O₂ does not form.
   • C: Oxygen is not released, and BH₃ is not a stable product.
   • D: B₂O₃ forms on burning in oxygen, not with water.

   Remember this

   Diborane gives boric acid and H₂ with water, but B₂O₃ and water when burnt in oxygen.

2. Question 2 · Medium

   Arrange the following Group 13 elements in increasing order of atomic radius. A. Al B. B C. Ga D. In

   1. AB, C, A, D
   2. BC, B, A, D
   3. CB, A, C, D
   4. DD, A, C, B

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   Answer: A · B, C, A, D

   Radii are about B 85, Ga 135, Al 143 and In 167 pm. Gallium is smaller than aluminium because its 3d electrons shield the nuclear charge poorly.

   • B: This places Ga below B, far too small for a fourth-period element.
   • C: This follows a simple group trend and misses the Ga and Al exception.
   • D: This is the decreasing order.

   Remember this

   Atomic radius rises down Group 13, except that Ga is smaller than Al because of poor 3d shielding.

3. Question 3 · Medium

   Given below are two statements: Statement I: In graphite, each carbon atom is sp² hybridised and the layers are held together by van der Waals forces. Statement II: Buckminsterfullerene, C₆₀, contains twenty six-membered rings and twelve five-membered rings. Choose the correct answer.

   1. ABoth Statement I and Statement II are incorrect
   2. BBoth Statement I and Statement II are correct
   3. CStatement I is incorrect but Statement II is correct
   4. DStatement I is correct but Statement II is incorrect

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   Answer: B · Both Statement I and Statement II are correct

   Graphite has flat sheets of sp² carbon with weak forces between layers, which is why it is soft and slippery. C₆₀ has a soccer-ball shape with 20 hexagons and 12 pentagons. Both statements are true.

   • A: Both statements match the known structures.
   • C: Statement I is also correct, as graphite layers are weakly held.
   • D: Statement II is also correct, as C₆₀ has both ring sizes.

   Remember this

   Weak forces between graphite layers make it a lubricant; delocalised electrons make it a conductor.

4. Question 4 · Hard

   SiCl₄ reacts with water, whereas CCl₄ is not hydrolysed. Which option gives the correct product and reason?

   1. ACCl₄ reacts faster than SiCl₄, because the small carbon atom attracts a lone pair from water
   2. BCCl₄ gives C(OH)₄ and HCl, because vacant 2d orbitals of carbon accept a lone pair from water
   3. CSiCl₄ gives SiO₂ and Cl₂, because the Si-Cl bond breaks homolytically on contact with water
   4. DSiCl₄ gives Si(OH)₄ and HCl, because vacant 3d orbitals of silicon accept a lone pair from water

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   Answer: D · SiCl₄ gives Si(OH)₄ and HCl, because vacant 3d orbitals of silicon accept a lone pair from water

   The oxygen of water donates a lone pair into a vacant 3d orbital of silicon, forming an intermediate, and HCl is then lost stepwise to give Si(OH)₄. Carbon has no d orbitals in its valence shell, and the small carbon is crowded by four chlorine atoms, so CCl₄ does not react.

   • A: This reverses the observed behaviour, as CCl₄ does not react.
   • B: The second shell has no d subshell, and CCl₄ is not hydrolysed.
   • C: Hydrolysis gives HCl, not Cl₂, and no homolysis occurs.

   Remember this

   Second-period carbon lacks valence d orbitals; this explains many differences from silicon, including the maximum covalency of four.

5. Question 5 · Easy

   How many three-centre two-electron bonds are present in a molecule of diborane, B₂H₆?

   1. A1
   2. B6
   3. C4
   4. D2

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   Answer: D · 2

   Two hydrogen atoms bridge the boron atoms, and each B-H-B unit is a three-centre two-electron bond. The other four hydrogens are terminal, with normal two-centre bonds.

   • A: This counts only one of the two bridges.
   • B: This counts all the B-H links as three-centre bonds.
   • C: This counts the terminal two-centre B-H bonds.

   Remember this

   Diborane has 4 terminal B-H bonds and 2 B-H-B banana bonds.

6. Question 6 · Medium

   Consider these statements about group 14 elements: A. Carbon forms pπ–pπ multiple bonds with itself and with oxygen and nitrogen. B. Silicon shows catenation more readily than carbon. C. The maximum covalency of carbon is four. D. The +2 oxidation state becomes more stable down the group. Choose the correct answer from the options given below.

   1. AA, B and D only
   2. BA, C and D only
   3. CB, C and D only
   4. DA and C only

   Answer and explanation in LearnFree account

7. Question 7 · Easy

   Down group 13, the +1 oxidation state becomes more stable because of the inert pair effect. Which element forms the most stable +1 compounds?

   1. AGa
   2. BTl
   3. CB
   4. DAl

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8. Question 8 · Hard

   Given below are two statements: Statement I: SnCl₂ is a poor reducing agent because +2 is the more stable oxidation state of tin. Statement II: Tl³⁺ compounds act as oxidising agents because +1 is the more stable oxidation state of thallium. Choose the correct answer.

   1. AStatement I is incorrect but Statement II is correct
   2. BBoth Statement I and Statement II are incorrect
   3. CStatement I is correct but Statement II is incorrect
   4. DBoth Statement I and Statement II are correct

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9. Question 9 · Medium

   Assertion A: Gallium has a larger atomic radius than aluminium. Reason R: In gallium, the ten 3d electrons shield the outer electrons poorly, so these electrons feel a higher effective nuclear charge. Choose the correct answer.

   1. AA is correct but R is not correct
   2. BBoth A and R are correct and R is the correct explanation of A
   3. CBoth A and R are correct but R is not the correct explanation of A
   4. DA is not correct but R is correct

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10. Question 10 · Hard

    Diborane is prepared by the reaction 4BF₃ + 3LiAlH₄ → 2B₂H₆ + 3LiF + 3AlF₃, and it is hydrolysed by water to boric acid and hydrogen. How many moles of LiAlH₄ are needed to make enough diborane to give 12 mol of H₂ on complete hydrolysis?

    1. A3 mol
    2. B18 mol
    3. C6 mol
    4. D2 mol

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11. Question 11 · Easy

    Boric acid, B(OH)₃, behaves as a weak monobasic acid in water because it

    1. Aaccepts a hydroxide ion from water, acting as a Lewis acid
    2. Breleases hydroxide ions as a weak base would
    3. Creleases one proton from one of its three B–OH groups
    4. Ddonates all three protons one after another

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12. Question 12 · Medium

    Match List-I with List-II. List-I (Substance) A. Diamond B. Graphite C. Fullerene C₆₀ D. ZSM-5 List-II (Feature) I. Layers of sp² carbon; conducts electricity II. Rigid three-dimensional network of sp³ carbon III. Cage of twenty six-membered and twelve five-membered rings IV. Zeolite that converts alcohols directly into gasoline Choose the correct answer from the options given below.

    1. AA-I, B-II, C-III, D-IV
    2. BA-II, B-I, C-III, D-IV
    3. CA-II, B-I, C-IV, D-III
    4. DA-II, B-III, C-I, D-IV

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13. Question 13 · Easy

    In diamond, each carbon atom is bonded tetrahedrally to four other carbon atoms. The hybridisation of carbon in diamond is

    1. Asp³d
    2. Bsp³
    3. Csp
    4. Dsp²

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14. Question 14 · Hard

    Consider these statements about group 14 elements. A. CO₂ is a gas, while SiO₂ is a network solid, because carbon forms pπ–pπ multiple bonds with oxygen and silicon does not. B. Diamond is a good conductor of electricity. C. Fullerene C₆₀ contains 20 five-membered and 12 six-membered rings. D. Carbon shows a maximum covalency of four, while silicon can expand its covalency to six, as in [SiF₆]²⁻. Choose the correct answer from the options given below.

    1. AA and D only
    2. BA, B and D only
    3. CA, C and D only
    4. DB and C only

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15. Question 15 · Medium

    Arrange the group 14 elements below by the stability of their +2 oxidation state, from least to most stable. A. Pb B. Si C. Sn D. Ge

    1. AB, D, C, A
    2. BD, B, C, A
    3. CA, C, D, B
    4. DB, C, D, A

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16. Question 16 · Medium

    Given below are two statements: Statement I: The atomic radius of gallium is smaller than that of aluminium. Statement II: The maximum covalency of boron is four, whereas aluminium can show a covalency of six, as in [AlF₆]³⁻. Choose the correct answer.

    1. ABoth Statement I and Statement II are correct
    2. BStatement I is correct but Statement II is incorrect
    3. CBoth Statement I and Statement II are incorrect
    4. DStatement I is incorrect but Statement II is correct

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17. Question 17 · Medium

    Aluminium dissolves in aqueous sodium hydroxide with effervescence. Which option gives the aluminium-containing product and the gas evolved?

    1. AAl₂O₃ and H₂
    2. BNaAlO₂ and O₂
    3. CAl(OH)₃ and O₂
    4. DNa⁺[Al(OH)₄]⁻ and H₂

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