Boron, the first member of group 13 (p-block) is a typical non-metal. H exists in two allotropic forms. The compounds of boron are mainly electron deficient as well as Lewis acids. For example, all the trihalides of boron `(BX_(3))` are Lewis acids. The expected order of acidic strength based on the electro negativity of halogen atoms is : `BF_(3)gtBC l_(3)gtBBr_(3)gtBl_(3)`. But the actual order is the reverse. This is explained with the help of the concept of back bonding `(p pi- p pi)` . Among the hydrides of boron. diborane has a bridged structure. Which of the following statements of group 13, the one which is most acidic is:A. `BCl_(3)` is a covalent compoundB. `BCl_(3)` acts as a Lewis acidC. `BCl_(3)` does not form a dimerD. In `BCl_(3)`, the B-Cl bond length is greater thatn the bond length of single covalent b ond.

Boron, the first member of group 13 (p-block) is a typical non-metal.

1.	Boron, the first member of group 13 (p-block) is a typical non-metal. H exists in two allotropic forms. The compounds of boron are mainly electron deficient as well as Lewis acids. For example, all the trihalides of boron `(BX_(3))` are Lewis acids. The expected order of acidic strength based on the electro negativity of halogen atoms is : `BF_(3)gtBC l_(3)gtBBr_(3)gtBl_(3)`. But the actual order is the reverse. This is explained with the help of the concept of back bonding `(p pi- p pi)` . Among the hydrides of boron. diborane has a bridged structure. Which of the following statements of group 13, the one which is most acidic is:A. `BCl_(3)` is a covalent compoundB. `BCl_(3)` acts as a Lewis acidC. `BCl_(3)` does not form a dimerD. In `BCl_(3)`, the B-Cl bond length is greater thatn the bond length of single covalent b ond.
Answer» B-Cl bond length is lesser than that of actual bond length of a pure single bond because the bond has a partial double bond character on account of back bonding.

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