Question

Which of the following is an incorrect statement about the compounds of group 13 elements?

• A. All the trihalides exist except TlI₃
• B. Trihalides on hydrolysis form tetrahedral species
• C. Diborane is an example of electron precise hydride
• D. Hydrolysis of diborane gives boric acid

Hint:

Remember the classification of covalent hydrides by the group number of the central element: Group 13 hydrides are electron-deficient, Group 14 are electron-precise, and Groups 15-17 are electron-rich. Diborane (Group 13) is the most famous electron-deficient hydride.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question tests the knowledge of the chemical properties of Group 13 elements (Boron family) and their compounds, specifically their halides and hydrides.
Step 2: Analyzing Each Statement:
- (A) All the trihalides exist except TlI₃: This statement is correct. Thallium triiodide (TlI₃) is unstable because the Tl³⁺ ion is a strong oxidizing agent, while the iodide ion (I⁻) is a reasonably strong reducing agent. They undergo an internal redox reaction. TlI₃ actually exists as an ionic compound of thallium(I) and the triiodide ion, Tl⁺(I₃)⁻.
- (B) Trihalides on hydrolysis form tetrahedral species: This statement is generally incorrect. For example, BCl₃ hydrolyzes to form planar boric acid, B(OH)₃. AlCl₃ hydrolyzes in water to form the octahedral aqua complex, \([Al(H₂O)_6]^{3+}\). While boron halides can form tetrahedral adducts like \([BF_4]^-\) or \([B(OH)_4]^-\) under certain conditions, it is not the universal product of simple hydrolysis. However, let's evaluate other options before concluding.
- (C) Diborane is an example of electron precise hydride: This statement is definitively incorrect. Diborane (B₂H₆) is the archetypal example of an electron-deficient hydride. The boron atoms in diborane do not have a complete octet of electrons; they are linked by three-center-two-electron "banana bonds". Electron-precise hydrides are formed by Group 14 elements (e.g., CH₄), where the central atom has a complete octet.
- (D) Hydrolysis of diborane gives boric acid: This statement is correct. Diborane reacts vigorously with water to produce boric acid and hydrogen gas. The reaction is: \(B_2H_6 + 6H_2O \rightarrow 2B(OH)_3 + 6H_2\).
Step 3: Identifying the Incorrect Statement:
Comparing the statements, statement (C) makes a fundamental classification error. Diborane is a classic example of an electron-deficient compound, not electron-precise. While statement (B) is also not universally true, statement (C) is unambiguously incorrect.
Step 4: Final Answer:
The incorrect statement is that diborane is an example of an electron precise hydride. Therefore, option (C) is the correct answer.