The reaction that is not feasible is the second one: Cl2 + 2NaF → 2NaCI + F2. This is because fluorine (F2) is a more reactive halogen than chlorine (Cl2), and as such it cannot be displaced from a compound like NaF by chlorine. This is an example of the reactivity series of halogens, where the more reactive halogens displace the less reactive halogens from their compounds.