JEE Main Chemistry question

The order of acidic strength of boron trihalides [Kerala CEE 2005, AMU 2005]

(A)BF_3 < BCl_3 < BBr_3 < BI_3Correct
(B)BI_3 < BBr_3 < BCl_3 < BF_3
(C)BCl_3 < BBr_3 < BI_3 < BF_3
(D)BBr_3 < BCl_3 < BI_3 < BF_3

Answer: (A)

Solution

Lewis acidity of boron trihalides increases as – back-bonding from halogen to boron's empty orbital weakens, which is strongest for F (comparable orbital size) and weakest

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Question ID VK-138261