Question 1

Which of the following statements best explains why boron forms only covalent compounds, while aluminium can form ionic compounds?

Accepted Answer

The sum of the first three ionisation enthalpies of boron is very high, preventing the formation of $$B^{3+}$$ ions and favoring covalent bonding.

Question 2

Which of the following best describes the trend in the stability of the +1 oxidation state in group 13 elements from aluminium to thallium?

Accepted Answer

The +1 oxidation state becomes more stable down the group due to the inert pair effect.

Question 3

Which property of graphite allows it to be used as a lubricant in high-temperature machinery?

Accepted Answer

Its layered structure with weak van der Waals forces between layers, allowing layers to slide over each other.

Question 4

Why is boric acid, $$\mathrm{H_3BO_3}$$, considered a weak acid?

Accepted Answer

It acts as a Lewis acid by accepting $$\mathrm{OH^-}$$ ions from water, rather than donating protons directly.

Question 5

Which of the following best explains why $$\mathrm{BF_3$}$$ acts as a strong Lewis acid?

Accepted Answer

Boron in $$\mathrm{BF_3$}$$ has an incomplete octet and readily accepts electron pairs.

Question 6

Which of the following reactions demonstrates the amphoteric nature of aluminium?

Accepted Answer

$$\mathrm{2Al(s) + 2NaOH(aq) + 6H_2O(l) \rightarrow 2Na^+[Al(OH)_4]^-(aq) + 3H_2(g)}$$

Question 7

Which of the following best explains why $$\mathrm{$$CCl_4$$} is $$not hydrolyzed by water, while $$\mathrm{$$SiCl_4$$} is $$readily hydrolyzed?

Accepted Answer

Carbon lacks available d orbitals to accommodate lone pairs from water, while silicon can use its vacant d orbitals.

Question 8

Which of the following statements about the structure of diborane ($$\mathrm{B_2H_6}) is $$correct?

Accepted Answer

Diborane contains two three-center two-electron (banana) bonds involving bridging hydrogen atoms.

Question 9

Which of the following best describes the trend in catenation among group 14 elements?

Accepted Answer

The tendency for catenation decreases down the group due to decreasing bond enthalpy and increasing atomic size.

Question 10

Which of the following is a correct statement about the acid-base nature of the oxides of group 14 elements?

Accepted Answer

$$CO_2$$ and $$SiO_2$$ are acidic, $$SnO_2$$ and $$PbO_2$$ are amphoteric.

Question 11

Which of the following statements about the electronic configuration and bonding of group 13 elements is correct?

Accepted Answer

Heavier group 13 elements have d and f electrons in their inner core, affecting their atomic radii and chemical properties.

Question 12

Which of the following best explains why $$\mathrm{[$$SiF_6$$]^{2-}}$$ exists but $$\mathrm{[$$SiCl_6$$]^{2-}}$$ does not?

Accepted Answer

Fluoride ions are smaller and can be accommodated around $$Si^{4+}$$, while chloride ions are too large.

Question 13

Which of the following is a correct statement about the toxicity of carbon monoxide ($$\mathrm{CO}$$)?

Accepted Answer

CO is toxic because it forms a stable complex with haemoglobin, preventing oxygen transport.

Question 14

Which of the following best describes the bonding and structure in diamond?

Accepted Answer

Each carbon atom is $$sp^3$$ hybridized and forms four sigma bonds in a tetrahedral arrangement.

Question 15

Which of the following is a correct real-world application of zeolites?

Accepted Answer

Zeolites are used as catalysts in petrochemical industries for cracking hydrocarbons and as ion exchangers for water softening.

Question 16

Which of the following statements about the hydrolysis of trihalides of group 13 elements is correct?

Accepted Answer

Trihalides of group 13 elements are covalent and are hydrolyzed in water to form tetrahedral $$[M(OH)_4]^-$$ species.

Question 17

Which of the following best explains why gallium has a smaller atomic radius than aluminium, despite being below it in the periodic table?

Accepted Answer

The presence of 10 d-electrons in gallium provides poor shielding, resulting in a higher effective nuclear charge and smaller atomic radius.

Question 18

Which of the following is a correct statement about the hybridization of boron in $$\mathrm{BF_3$}$$ and $$\mathrm{[BH_4$]^-}$$?

Accepted Answer

Boron is $$sp^2$$ hybridized in $$\mathrm{BF_3$}$$ and $$sp^3$$ hybridized in $$\mathrm{[BH_4$]^-}.$$

Question 19

Which of the following best describes the structure and bonding in fullerenes (e.g., $$\mathrm{C_{60}}$$)?

Accepted Answer

$$\mathrm{C_{60}} is a $$spherical molecule with $$sp^2$$ hybridized carbon atoms forming both five- and six-membered rings.

Study Notes: The p-Block Elements (Groups 13 and 14) – Boron and Carbon Families

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