Answer
$F^-$ is a Lewis base.
Work Step by Step
- The element $F$ has, naturally, 7 electrons in its valence shell.
- $F^-$ has one negative charge: 7 + 1 = 8 electrons, where none of them are being used.
- Therefore, $F^-$ is capable of donating these electrons to create bonds, so, this is a Lewis base.
** We know that it doesn't have insignificant basicity because, its conjugate acid: $HF$ is a weak acid, which means that $F^-$ is a weak base too.
