Which from following is a weak field ligand?

The strength of a ligand is determined by its position in the spectrochemical series, which orders ligands by their crystal field splitting ability.

The comparative order of relevant ligands is: $\text{F}^- < \text{NH}_3 < \text{EDTA}^{4-} < \text{CO}$.

$\text{F}^-$ is a weak field ligand due to its position at the weaker end of the spectrochemical series, while the others exhibit stronger field characteristics.
Carbonyl ($\text{CO}$) is particularly strong due to its $\pi$-acceptor properties.

The weakest field ligand among the options is $\boxed{\text{C}}$.