This collection of BPSC PGT Chemistry MCQs focuses on “p-Block Elements – Important Trends and Anomalous Properties of Boron”, covering key concepts for exam preparation.

1. Group 13 hydrides are formed directly.
   a) true
   b) false

Answer: (b)
Explanation: Group 13 elements do not react directly with hydrogen to form hydrides; instead, their hydrides are synthesized through indirect methods. For example, diborane (B₂H₆) is produced when boron fluoride (BF₃) reacts with lithium aluminum hydride (LiAlH₄) in the presence of dry ether.

2. All the oxides and hydroxides of Boron family are ____________ in nature.
   a) acidic
   b) basic
   c) acidic and basic
   d) acidic, basic and amphoteric

Answer: (d)
Explanation: As we move down the group in Group 13, the oxides and hydroxides transition from acidic to amphoteric and eventually basic in nature. Among them, only boric acid is soluble in water, while the hydroxides of other elements remain insoluble.

3. Which of the following is a colourless gas?
   a) Boron chloride
   b) Boron fluoride
   c) Boron Bromide
   d) Boron iodide 

Answer: (b)
Explanation: All boron halides exist as trihalides (BX₃). Boron chloride (BCl₃) and boron bromide (BBr₃) are colorless, fuming liquids, while boron fluoride (BF₃) is a colorless gas, and boron iodide (BI₃) is a white solid at room temperature. All these trihalides act as Lewis acids.

4. Which of the following is true regarding the acidic character?
   a) Aluminium halides acidic character is greater than that of indium halide
   b) Boron halide acidic character is less than that of gallium halide
   c) Gallium halides acidic character is less than that of indium halide
   d) Aluminium halides acidic character is greater than that of boron halide 

Answer: (a)
Explanation: The halides of Group 13 elements act as Lewis acids, with their acidic character decreasing in the order: Boron > Aluminium > Gallium > Indium. Here, halide refers to chlorides, bromides, and iodides. However, thallium trichloride (TlCl₃) primarily acts as an oxidizing agent as it readily decomposes.

5. Which of the following compound is formed when aluminium reacts with an alkali?
   a) sodium Tetra hydroxyl aluminate V
   b) sodium Tetra hydroxyl aluminate III
   c) sodium Penta hydroxyl aluminate IV
   d) sodium Septa hydroxyl aluminate III

Answer: (b)
Explanation: When 2 moles of aluminum (Al) react with 2 moles of sodium hydroxide (NaOH) in the presence of 6 moles of water (H₂O), it forms 2 moles of sodium tetrahydroxoaluminate(III) [Na[Al(OH)₄]] along with 3 moles of hydrogen gas (H₂).

6. Which of the following element has the highest melting point?
   a) thallium
   b) gallium
   c) aluminium
   d) boron

Answer: (d)
Explanation: Boron has a significantly higher melting point than other Group 13 elements due to its three-dimensional network structure, where boron atoms are strongly bonded by covalent bonds. This strong bonding also results in a higher boiling point compared to the rest of the group.

7. ____________ and Boron are same in case when reacted with concentrated nitric acid.
   a) Oxygen
   b) Aluminium
   c) Hydrogen
   d) No other metal

Answer: (d)
Explanation: Boron reacts with concentrated nitric acid, forming boric acid and nitrous oxide. In contrast, aluminum becomes passive in nitric acid due to the formation of a protective oxide layer on its surface, preventing further oxidation.

8. Which of the following is the correct reason for the anomalous behaviour of Boron?
   a) low ionization energy
   b) smallest size in the group
   c) low electronegativity
   d) the presence of the orbital and can show allotropy

Answer: (b)
Explanation: Boron exhibits anomalous behavior compared to other Group 13 elements due to its smallest atomic size, highest ionization energy, highest electronegativity, absence of vacant d-orbitals, and presence of allotropes, which are not observed in the other group members.

9. Boron shows a diagonal relationship with ____________
   a) thallium
   b) lithium
   c) magnesium
   d) aluminium

Answer: (c)
Explanation: Boron (B) exhibits a diagonal relationship with magnesium (Mg) in the periodic table. This similarity arises due to their comparable charge densities, electronegativities, and atomic/ionic radii, which is a common trend for diagonally adjacent elements in the periodic table.

10. Do Boron and silicon react with electropositive metals?
    a) Yes
    b) No
    c) Maybe
    d) May not be

Answer: (a)
Explanation: Both boron and silicon form covalent hydrides, known as boranes and silanes, respectively. They react with electropositive metals to produce binary compounds, which yield a mixture of boranes and silanes upon hydrolysis.

11. Which of the following property is not a similarity between Boron and silicon?
    a) metals
    b) non-metals metals
    c) semiconductors
    d) formation of covalent hydrides

Answer: (a)
Explanation: Boron of group 13 and silicon of group 14 share a diagonal relationship and have many similarities. Both boron and silicon are non-metals, semiconductors and they also form covalent hydrides, therefore, they are not metals.

12. Boron and silicon form covalent and volatile halides.
    a) true
    b) false

Answer: (a)
Explanation: Both boron of group 13 and silicon of group 14 form covalent and volatile halides, which fume in moisture air due to the release of HCl gas. They react with water in order to form boric acid and silicon hydroxide along with hydrochloric gas which is volatile in nature.

13. ____________ Boron is reactive with air.
    a) Neither crystalline nor amorphous
    b) Crystalline
    c) Both crystalline and amorphous
    d) Amorphous

Answer: (d)
Explanation: Crystalline boron is unreactive, whereas amorphous boron is highly reactive. When heated to 700°C in air, boron reacts separately with oxygen and nitrogen, forming boron oxide and boron nitride, respectively.

14. Which of the following elements do you think can react with water?
    a) Thallium
    b) Boron
    c) Aluminium
    d) Gallium

Answer: (a)
Explanation: Boron and aluminium do not react with water under normal conditions. However, amalgamated aluminium reacts with water, releasing hydrogen gas. Gallium and indium remain unreactive with both cold and hot water, whereas thallium forms an oxide layer on its surface.

15. Which of the following elements is more reactive with air?
    a) indium
    b) gallium
    c) thallium
    d) all three are equally reactive

Answer: (c)
Explanation: Thallium is more reactive than gallium and indium due to its tendency to form a stable unipositive ion (Tl⁺). It readily reacts with oxygen in the air to form thallium(I) oxide (Tl₂O), which is more stable than thallium(III) oxide (Tl₂O₃) due to the inert pair effect.