Which of the following shows correct Lewis acidic strength order of trihalides of boron ?
| A. |
`BCl_3 > BBr_3 > BF_3 > Bl_3` |
| B. |
`BF_3 < BBr_3 < BCl_3 < Bl_3` |
| C. |
`BF_3 < BCl_3 < BBr_3 < Bl_3` |
 |
| D. |
`BF_3 > BCl_3 > BBr_3 > Bl_3` |
This cannot be explained on the basis of electronegativity of substituent attached actually. This can be explained on te basis of `p_(pi)-p_(pi)` back bonding, greater the `p_(pi)-p_(pi)` back bonding lower is its lewis acidic strength.
`rarr` Back bonding tendency decreases
`rarr` Lewis acidity increases