Which of the following trihalides of boron acts as the strongest Lewis acid? — p Block Elements Chemistry Question

💡 Solution & Explanation

The Lewis acid strength increases in the order $BF_3 < BCl_3 < BBr_3 < BI_3$. The effectiveness of $p\pi-p\pi$ back bonding decreases as the size of the halogen atom increases from F to I, leaving the boron atom more electron-deficient in $BI_3$.