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: Analyze Statement C: Diborane (\( \text{B}_2\text{H}_6 \)) is a hydride of Boron (Group 13). Group 13 elements have only 3 valence electrons. Even in the dimer form, there are not enough electrons to form normal 2-center-2-electron bonds for the bridge hydrogens (3-center-2-electron bonds are formed). Therefore, it is classified as an electron-deficient hydride, not electron precise. Electron precise hydrides belong to Group 14 (e.g., \( \text{CH}_4 \)).
Step 2: Analyze other statements: (A) Correct. \( \text{TlI}_3 \) does not exist (or exists as \( \text{Tl}^+ \text{I}_3^- \)) because Thallium shows a stable +1 oxidation state due to the inert pair effect, and \( \text{I}^- \) is a strong reducing agent which reduces \( \text{Tl}^{3+} \). (B) Correct. For example, \( \text{BCl}_3 \) hydrolyses to form \( [\text{B}(\text{OH})_4]^- \) which is tetrahedral. (D) Correct. \( \text{B}_2\text{H}_6 + 6\text{H}_2\text{O} \to 2\text{H}_3\text{BO}_3 + 6\text{H}_2 \). Boric acid is formed. Conclusion: Statement (C) is incorrect.