The p-Block Elements (Group 13 and 14) - MCQs with Explanations

1. In Goldschmidt aluminothermic process, the reducing agent used is:

• (a) coke
• (b) Al powder
• (c) Na
• (d) Ca

Correct Answer: (b)

Explanation: Aluminium powder is utilized as a reducing agent in the thermite process.

2. The electronic configurations of four elements are given below. Which element does not belong to the same family?

• (a) [Xe] 4f¹⁴ 5d¹⁰ 6s²
• (b) [Kr] 4d¹⁰ 5s²
• (c) [Ne] 3s² 3p⁵
• (d) [Ar] 3d¹⁰ 4s²

Correct Answer: (c)

Explanation: The electronic configuration in option (c) represents a p-block element (Halogen family), whereas the others belong to different blocks (Group 2 or d-block).

3. Which of the following does not exist in free form?

• (a) BF₃
• (b) BH₃
• (c) BCl₃
• (d) BBr₃

Correct Answer: (b)

Explanation: While boron forms hydrides with the general formula B_nH_n+4, BH₃ is unstable and exists as the dimer B₂H₆.

4. In diborane, the "banana bond" is formed between:

• (a) 2 electrons, 3 atoms
• (b) 2 electrons, 1 atom
• (c) 2 electrons, 2 atoms
• (d) 1 electron, 2 atoms

Correct Answer: (a)

Explanation: This is a three-center two-electron bond (3c-2e) involving two boron nuclei and one hydrogen nucleus.

5. The formula of corundum is:

• (a) Al₂O₃
• (b) Al₂O₃ · H₂O
• (c) Al₂O₃ · 2H₂O
• (d) Al₂O₃ · 3H₂O

Correct Answer: (a)

Explanation: Corundum is the anhydrous form of aluminium oxide, Al₂O₃.

6. Match the column I with column II:
(A) Used as lubricant; (B) 3D oxide structure; (C) Used in solar cells; (D) Anhydride of carbonic acid.

• (a) (A)->(iv), (B)->(iii), (C)->(ii), (D)->(i)
• (b) (A)->(iv), (B)->(i), (C)->(iii), (D)->(i)
• (c) (A)->(iii), (B)->(ii), (C)->(i), (D)->(iv)
• (d) (A)->(ii), (B)->(iii), (C)->(iv), (D)->(i)

Correct Answer: (d)

Explanation: Graphite (ii) is a lubricant; Silica (iii) has a 3D structure; Silicone (iv) is used in solar cells; and CO₂ (i) is the anhydride of carbonic acid.

7. Which of the following is not easily hydrolysed?

• (a) CCl₄
• (b) SiCl₄
• (c) SnCl₄
• (d) PbCl₄

Correct Answer: (a)

Explanation: CCl₄ cannot be hydrolysed easily because carbon lacks d-orbitals, preventing it from extending its coordination number to accommodate water molecules.

8. Which of the following oxides is basic?

• (a) SiO₂
• (b) SnO₂
• (c) CO₂
• (d) Li₂O

Correct Answer: (d)

Explanation: SiO₂ and CO₂ are acidic; SnO₂ is amphoteric; and Li₂O is a basic oxide.

9. The main factor responsible for the acidic nature of BF₃ is:

• (a) pπ-dπ back-bonding
• (b) three centre-electron bonds
• (c) large electronegativity of F
• (d) pπ-pπ back-bonding

Correct Answer: (d)

Explanation: The pπ-pπ back-bonding from fluorine to boron reduces the electron deficiency, but boron halides remain Lewis acids. Smaller atoms exhibit more effective back-bonding.

10. Which among the following has the tendency to form covalent compounds?

• (a) Calcium
• (b) Beryllium
• (c) Strontium
• (d) Magnesium

Correct Answer: (b)

Explanation: Beryllium tends to form covalent salts due to its small ionic size and high ionization enthalpy.

11. Which one of the following is incorrect?

• (a) Boron halides are all monomeric while those of Al are dimeric.
• (b) Boron halides and aluminium halides exist as monomeric halides.
• (c) Boron halides and aluminium halides are Lewis acids.
• (d) B₂O₃ alone is acidic while Al₂O₃ is amphoteric.

Correct Answer: (b)

Explanation: Trihalides of boron are monomeric, whereas aluminium halides like AlCl₃ exist as dimers (Al₂Cl₆).

12. Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out:

• (a) in the presence of NaCl
• (b) in the presence of fluorite
• (c) in the presence of cryolite which forms a melt with lower melting temperature
• (d) in the presence of cryolite which forms a melt with higher melting temperature

Correct Answer: (c)

Explanation: Cryolite is added to lower the melting point of the alumina and increase its electrical conductivity.

13. Which of the following hydroxides is acidic in nature?

• (a) Be(OH)₂
• (b) Mg(OH)₂
• (c) B(OH)₃
• (d) Al(OH)₃

Correct Answer: (c)

Explanation: Boric acid, B(OH)₃ (or H₃BO₃), acts as a weak monobasic acid in aqueous solution.

14. AlCl₃ is a:

• (a) weak protonic acid
• (b) strong protonic acid
• (c) Lewis acid
• (d) Lewis base

Correct Answer: (c)

Explanation: AlCl₃ is an electron-deficient molecule and acts as a Lewis acid by accepting an electron pair.

15. Arrange CCl₄, AlCl₃, PCl₅ and SiCl₄ according to ease of hydrolysis:

• (a) CCl₄ < SiCl₄ < PCl₅ < AlCl₃
• (b) AlCl₃ < CCl₄ < PCl₅ < SiCl₄
• (c) CCl₄ < AlCl₃ < PCl₅ < SiCl₄
• (d) CCl₄ < AlCl₃ < SiCl₄ < PCl₅

Correct Answer: (d)

Explanation: The ease of hydrolysis follows the order CCl₄ < AlCl₃ < SiCl₄ < PCl₅.

16. In silicon dioxide:

• (a) each silicon atom is surrounded by four oxygen atoms and each oxygen atom is bonded to two silicon atoms
• (b) each silicon atom is surrounded by two oxygen atoms and each oxygen atom is bonded to two silicon atoms
• (c) silicon atom is bonded to two oxygen atoms
• (d) there are double bonds between silicon and oxygen atoms

Correct Answer: (a)

Explanation: Silica exists in a 3D network where each Si is tetrahedrally bonded to four O atoms, and each O is shared by two Si atoms.

17. Which is/are true statements?

• (a) Diamond is unaffected by conc. acids but graphite reacts with hot conc. HNO₃.
• (b) CO is toxic because it forms a complex with haemoglobin.
• (c) C₃O₂ is a foul-smelling gas.
• (d) All are true statements.

Correct Answer: (d)

Explanation: Graphite is reactive due to its mobile electrons; CO forms carboxyhaemoglobin; and C₃O₂ is foul-smelling.

18. In the reaction B₂O₃ + C + Cl₂ → A + CO, compound A is:

• (a) CCl₄
• (b) BCl₃
• (c) BCl₂
• (d) B₂Cl₂

Correct Answer: (b)

Explanation: The reduction and chlorination of boron trioxide yield boron trichloride.

19. The tendency of BF₃, BCl₃ and BBr₃ to behave as Lewis acids decreases in the sequence:

• (a) BCl₃ > BF₃ > BBr₃
• (b) BBr₃ > BCl₃ > BF₃
• (c) BBr₃ > BF₃ > BCl₃
• (d) BF₃ > BCl₃ > BBr₃

Correct Answer: (b)

Explanation: Due to decreasing pπ-pπ back-bonding efficiency from F to Br, the boron atom becomes more electron-deficient, making BBr₃ the strongest Lewis acid.

20. Which of the following shows a pattern of bonding in silicones?

• (a) Si-C-Si - O - Si
• (b) Si-C-Si - C - Si
• (c) Si-O-Si - O - Si
• (d) Si-Si-Si - Si

Correct Answer: (c)

Explanation: Silicones are characterized by the repeating -Si-O-Si- backbone.

21. The incorrect statement among the following is:

• (a) the first IE of Al is less than that of Mg.
• (b) the second IE of Mg is greater than that of Na.
• (c) the first IE of Na is less than that of Mg.
• (d) the third IE of Mg is greater than that of Al.

Correct Answer: (b)

Explanation: Na⁺ has a stable noble gas configuration; removing a second electron requires significantly more energy than removing the second electron from Mg⁺, which results in a stable configuration.

22. B₂H₆ consists of:

• (a) covalent and ionic bonds
• (b) covalent and 3-centre two-electron bonds
• (c) metallic and covalent
• (d) only covalent

Correct Answer: (b)

Explanation: Diborane contains four normal terminal B-H covalent bonds and two "bridge" 3-centre two-electron bonds.

23. The hydration energy of Mg²⁺ ions is higher than that of:

• (a) Al³⁺
• (b) Be²⁺
• (c) Na⁺
• (d) none of these

Correct Answer: (c)

Explanation: Small, highly charged cations have higher hydration energies. Mg²⁺ is smaller and more charged than Na⁺.

24. Borax bead consists of a transparent glassy mass of:

• (a) mixture of sodium metaborate and boric anhydride
• (b) boric anhydride
• (c) sodium metaborate
• (d) sodium pyroborate

Correct Answer: (a)

Explanation: Strong heating of borax yields sodium metaborate (NaBO₂) and boric anhydride (B₂O₃).

25. Dry powder fire extinguisher contains:

• (a) sand
• (b) sand and Na₂CO₃
• (c) sand and baking soda
• (d) sand and K₂CO₃

Correct Answer: (c)

Explanation: A mixture of silica sand and sodium bicarbonate is used in dry powder fire extinguishers.

26. Name the structure of silicate in which one oxygen atom of [SiO₄]^4- is shared?

• (a) Linear chain silicate
• (b) Sheet silicate
• (c) Pyrosilicate
• (d) Three dimensional

Correct Answer: (c)

Explanation: Pyrosilicates contain two units joined at one shared oxygen vertex.

27. The bonds present in borazole (B₃N₃H₆) are:

• (a) 9σ, 6π
• (b) 12σ, 3π
• (c) 6σ, 9π
• (d) 15σ only

Correct Answer: (b)

Explanation: Borazole has six B-N σ bonds, three B-H σ bonds, three N-H σ bonds, and three B-N π bonds.

28. Boron does not form B³⁺ ions whereas Al forms Al³⁺ ions because:

• (a) the size of B atom is smaller than that of Al
• (b) the sum of IE₁+IE₂+IE₃ of B is much higher than that of Al
• (c) the sum of IE₁+IE₂+IE₃ of Al is much higher than that of B
• (d) both (a) and (b)

Correct Answer: (d)

Explanation: The small size of boron leads to an exceptionally high cumulative ionization energy for its first three electrons.

29. Diamond is hard because:

• (a) all the four valence electrons are bonded to each carbon atom by covalent bonds
• (b) it is a giant molecule
• (c) it is made up of carbon atoms
• (d) it cannot be burnt

Correct Answer: (a)

Explanation: In diamond, each carbon is sp³ hybridized and linked to four others tetrahedrally by strong covalent bonds in a 3D network.

30. Which is not correct?

• (a) Ge(OH)₂ is amphoteric.
• (b) GeCl₂ is more stable than GeCl₄.
• (c) GeO₂ is weakly acidic.
• (d) GeCl₄ in HCl forms [GeCl₆]^2- ion.

Correct Answer: (b)

Explanation: For germanium, the +4 oxidation state is more stable than the +2 state; thus GeCl₄ is more stable than GeCl₂.

31. AlCl₃ is covalent while AlF₃ is ionic. This can be justified by:

• (a) valence bond theory
• (b) crystal structure
• (c) lattice energy
• (d) Fajan rule

Correct Answer: (d)

Explanation: According to Fajan's rule, the small fluoride ion is less polarizable, leading to ionic character, while the larger chloride ion is more easily polarized, leading to covalent character.

32. What occurs if excess dilute NaOH is added to an aqueous solution of AlCl₃?

• (a) A permanent white precipitate forms.
• (b) No change at first, but white ppt forms later.
• (c) A white precipitate forms and then dissolves.
• (d) A green precipitate forms.

Correct Answer: (c)

Explanation: Al(OH)₃ initially precipitates but dissolves in excess NaOH to form soluble sodium aluminate, NaAlO₂.

33. Which of the following exists as a dimer?

• (a) Aluminium chloride
• (b) Sodium bromide
• (c) Methyl iodide
• (d) Magnesium chloride

Correct Answer: (a)

Explanation: AlCl₃ exists as the dimer Al₂Cl₆.

34. A metal forms chlorides in +2 and +4 states. Which is correct?

• (a) MCl₂ is more soluble in ethanol than MCl₄.
• (b) MCl₂ is more volatile than MCl₄.
• (c) MCl₂ is more ionic than MCl₄.
• (d) MCl₂ is more easily hydrolysed.

Correct Answer: (c)

Explanation: Higher oxidation states increase polarizing power, making the bond more covalent. Thus, the lower state chloride is more ionic.

35. Extraction of aluminium from its oxide is best done by:

• (a) electrolytic reduction
• (b) reduction with carbon
• (c) reduction with sodium
• (d) reduction with CO

Correct Answer: (a)

Explanation: Aluminium is extracted via the electrolysis of alumina dissolved in molten cryolite.

36. Lead poisoning in the body can be removed by:

• (a) EDTA in the form of calcium dihydrogen salt
• (b) cis-platin
• (c) Zeisse's salt
• (d) DMG

Correct Answer: (a)

Explanation: EDTA acts as a chelating agent to remove heavy metal ions like lead from the body.

37. Quartz is an example of:

• (a) chain silicate
• (b) infinite sheet silicate
• (c) framework silicate
• (d) cyclic silicate

Correct Answer: (c)

Explanation: Quartz is a framework (three-dimensional) silicate where all four oxygen atoms of each SiO₄ tetrahedron are shared.

38. Aluminium on reaction with aqueous KOH solution gives:

• (a) KO₂ + H₂
• (b) KAlO₂ + H₂
• (c) K₂O + H₂
• (d) KAlO₂ + H₂O

Correct Answer: (b)

Explanation: This is the basis of Uyeno's method for preparing pure hydrogen.

39. Select the incorrect statement regarding the reactions involving BF₃, Al₂Cl₆, and B₂Cl₄:

• (a) The compound (A) is BCl₃.
• (b) The compound (C) is B₂(OH)₄.
• (c) The compound (C) is B(OH)₃.
• (d) The compound (B) is B₂Cl₄.

Correct Answer: (c)

Explanation: Hydrolysis of B₂Cl₄ (B) yields B₂(OH)₄ (C), making statement (c) incorrect.

40. In Goldschmidt aluminothermic process, thermite contains:

• (a) 3 parts of Fe₂O₃ and 2 parts of Al
• (b) 3 parts of Al₂O₃ and 4 parts of Al
• (c) 3 parts of Fe₂O₃ and 1 part of Al
• (d) 1 part of Fe₂O₃ and 1 part of Al

Correct Answer: (c)

Explanation: Thermite mixture consists of 3 parts iron oxide and 1 part aluminium powder.

41. Stability of dihalides of Si, Ge, Sn and Pb increases in the sequence:

• (a) GeX₂ << SiX₂ << SnX₂ << PbX₂
• (b) SiX₂ << GeX₂ << PbX₂ << SnX₂
• (c) SiX₂ << GeX₂ << SnX₂ << PbX₂
• (d) PbX₂ << SnX₂ << GeX₂ << SiX₂

Correct Answer: (c)

Explanation: Due to the inert pair effect, the stability of the +2 oxidation state increases down the group.

42. In SiF₆^2- and SiCl₆^2-, which one is known and why?

• (a) SiF₆^2- because of small size of F
• (b) SiF₆^2- because of large size of F
• (c) SiCl₆^2- because of small size of Cl
• (d) SiCl₆^2- because of large size of Cl

Correct Answer: (a)

Explanation: Silicon can accommodate six small fluoride ions around it to form a complex, but chloride ions are too large.

43. Identify A and B in: SnCl₂ + HgCl₂ → (A) + SnCl₄; (A) + SnCl₂ → (B) + SnCl₄:

• (a) HgCl₄, Hg
• (b) Hg₂Cl₂, Hg
• (c) SnCl₄, Sn
• (d) Sn₂Cl₂, Sn

Correct Answer: (b)

Explanation: SnCl₂ reduces HgCl₂ to white Hg₂Cl₂ (A), then to grey metallic Hg (B).

44. In graphite, additional electrons are:

• (a) localised on each C-atom
• (b) localised on every third C-atom
• (c) present in anti-bonding orbital
• (d) delocalised forming extended π-bonding system

Correct Answer: (d)

Explanation: One p-orbital electron on each sp² hybridized carbon is delocalized throughout the layer, making graphite conductive.

45. Which statement about zeolites is false?

• (a) Used as cation exchangers.
• (b) Have open structures to take up small molecules.
• (c) Are aluminosilicates with 3D network.
• (d) Some SiO₄^4- units are replaced by AlO₄^5- and AlO₆^9- ions.

Correct Answer: (d)

Explanation: In zeolites, some Si atoms in the 3D silica framework are replaced by Al³⁺ ions. Statement (d) is identified as false in the sources.