The correct option is (c) \(\mathrm{K}^{+}\)and \(\left[\mathrm{HF}_{2}\right]^{-} .\)
Explanation:
The fluoride ion, by a process of hydrogen bonding, forms the anion, \(\mathrm{HF}_{2}\). The compound is written as \(\mathrm{K}^{+}\left[\mathrm{HF}_{2}\right]\).