Question

Given below are two statements:
Statement I: The number of pairs among [SiO₂, CO₂], [SnO, SnO₂], [PbO, PbO₂] and [GeO, GeO₂], which contain oxides that are both amphoteric is 2.
Statement II: BF₃ is an electron deficient molecule, can act as a Lewis acid, forms adduct with NH₃ and has a trigonal planar geometry.
In the light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are false
• B. Statement I is true but Statement II is false
• C. Both Statement I and Statement II are true
• D. Statement I is false but Statement II is true

Hint:

For p-block elements, remember the trend in the nature of oxides. For non-metals (like C, Si), oxides are acidic. For metalloids (like Ge), they are amphoteric/acidic. For metals (like Sn, Pb), they are amphoteric. Also, the properties of BF₃ as a classic Lewis acid are a fundamental concept in chemical bonding.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to evaluate two statements. Statement I is about the chemical nature (acidic, basic, amphoteric) of Group 14 oxides. Statement II describes the properties of Boron Trifluoride (BF₃).
Step 2: Detailed Explanation:
Analysis of Statement I:
The statement claims that there are exactly two pairs where both oxides are amphoteric. Let's analyze the nature of the oxides in each pair. These are oxides of Group 14 elements (C, Si, Ge, Sn, Pb).
\begin{itemize} \item General Trend: Down Group 14, the stability of the +4 oxidation state decreases and the +2 state increases. The character of the oxides changes from acidic to amphoteric. \begin{itemize} \item CO₂: Acidic
\item SiO₂: Acidic
\item GeO₂: Amphoteric (mainly acidic)
\item SnO, SnO₂: Amphoteric
\item PbO, PbO₂: Amphoteric
\end{itemize} \item Pair 1: [SiO₂, CO₂]: Both are acidic oxides. This pair does not qualify.
\item Pair 2: [SnO, SnO₂]: Both SnO and SnO₂ are classic examples of amphoteric oxides. They react with both acids and strong bases. This pair qualifies.
\item Pair 3: [PbO, PbO₂]: Both PbO and PbO₂ are also classic examples of amphoteric oxides. This pair qualifies.
\item Pair 4: [GeO, GeO₂]: GeO₂ is considered amphoteric, though it has predominantly acidic character. The nature of GeO is less commonly discussed, but it is not typically classified as amphoteric. Therefore, this pair is unlikely to have both oxides being amphoteric.
\end{itemize} We have clearly identified two pairs, [SnO, SnO₂] and [PbO, PbO₂], where both oxides are amphoteric.
Conclusion: The statement that the number of such pairs is 2 is correct. Statement I is true.
Analysis of Statement II:
This statement makes several claims about Boron Trifluoride (BF₃). Let's check each one.
\begin{itemize} \item Electron deficient molecule: In BF₃, the central Boron atom forms three single bonds with three Fluorine atoms. It has only 6 valence electrons in its shell, not a full octet. Therefore, it is an electron-deficient molecule. This is true.
\item Can act as a Lewis acid: Because it is electron-deficient, the Boron atom has a vacant p-orbital and can accept a pair of electrons from a donor species (a Lewis base). This is the definition of a Lewis acid. This is true.
\item Forms adduct with NH₃: Ammonia (NH₃) has a lone pair of electrons on the Nitrogen atom, making it a Lewis base. It reacts with the Lewis acid BF₃ to form a coordinate covalent bond, resulting in the formation of an adduct, F₃B←NH₃. This is true.
\item Has a trigonal planar geometry: According to VSEPR theory, the central Boron atom has 3 bond pairs and 0 lone pairs. This arrangement minimizes repulsion, leading to a trigonal planar geometry with F-B-F bond angles of 120°. This is true.
\end{itemize} Since all the assertions within the statement are correct, the entire statement is true.
Conclusion: Statement II is true.
Step 3: Final Answer:
Both Statement I and Statement II are true. This corresponds to option (C).