Question

Which of the following halides have the highest basic strength?

• A. $F^{-}$
• B. $C{l}^{-}$
• C. $B{r}^{-}$
• D. $I^{-}$

Answer 1

The correct option is A $F^{-}$

$\text{Basic strength}\propto \frac{1}{\text{Acidic strength of conjugate acid}}$
The conjugate acids of the respective species are :
$HF,HCl,HBr,HI$
Down the group the electronegativity decreases and the size increases.
Thus, it becomes easy to lose $H^{+}$ ion. This causes the increase in acidic strength down the group.
Conjugate acids strength order :
$HI>HBr>HCl>HF$

Hence, the basic strength order is:
$F^{-}>C{l}^{-}>B{r}^{-}>I^{-}$

So (a) is the correct option.