Name the compound which is used to obtain fluorine gas on electrolysis. At which electrode does `F_2` appears?

Explanation

A Solution of potassium hydrogen fluoride `(KHF_2)` in anhydrous HF.
`KF+HF to K [HF_2] overset"electrolysis"to H_2 + F_2`
On Electrolysis :
Anode: `HF_2^(-) to F_2 + H^(+) + 2e^(-)`
Cathode: `2HF + H^(+) + 2e^(-) to H_2 + HF_2^-`