Q16 / 160 · TS EAMCET 2022 (19 Jul Shift 1) · Chemistry

The correct order of Lewis acidic character of boron trihaldes is

  • A
    $\mathrm{BF}_3>\mathrm{BCl}_3>\mathrm{BI}_3>\mathrm{BBr}_3$
  • B
    $\mathrm{BI}_3>\mathrm{BBr}_3>\mathrm{BF}_3>\mathrm{BCl}_3$
  • Correct answer
    C
    $\mathrm{BI}_3>\mathrm{BBr}_3>\mathrm{BCl}_3>\mathrm{BF}_3$
  • D
    $\mathrm{BF}_3>\mathrm{BCl}_3>\mathrm{BBr}_3>\mathrm{BI}_3$

Solution

On moving down the group, the size of atom increases and ability of back bonding decreases which makes them more acidic. Hence, the Lewis acidic character of boron halide is $\mathrm{BI}_3>\mathrm{BBr}_3>\mathrm{BCl}_3>\mathrm{BF}_3$.

Hence, the correct answer is option: 'C'.

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