Give reason to explain why $ClF_3$ exists but $FCl_3$ does not exist.

(N/A) Chlorine has vacant $3d$-orbitals in its valence shell,allowing it to expand its octet and exhibit a $(+3)$ oxidation state by promoting an electron to the $3d$ subshell. This enables the formation of $ClF_3$. In contrast,fluorine is the most electronegative element and lacks $d$-orbitals in its valence shell $(n=2)$. Therefore,it cannot exhibit positive oxidation states or expand its covalency beyond $1$,making the existence of $FCl_3$ impossible.