Question: why khcl2 is not possible?
Answer: due to small size of K it does not form KHcl2 and as fluorine is smaller it exist as KHf2. Fluorine ion by a process of hydrogen bonding forms the anion [HF2]-. This tendency is missing with other halides for lack of possibility of such strong intermolecular attraction. ... Hence it gives two series of salts KHF2 and KF.