Answer
Solution C, it will be slightly basic.
Work Step by Step
NaF is a molecular electrolyte and will dissociate in water giving as products the two ions $Na^+$ (sodium ion) and $F^-$ (fluoride). Fluoride is a weak base, its reaction with water will then be the following:
$F^-$+$H_{2}O$ ⇌ $HF$+$OH^-$
As we know, a weak base only ionizes partly, and thats why in the final solution [$F^-$] will be greater than [$HF$], but it will still be present.
The ions present in solution will then be: $Na^+$, $F^-$ and $OH^-$. The molecule $HF$ will also be present.
The solution will be slightly basic because of the reaction shown above and the proprieties of the fluoride ion.
