Which of the following, Fluorine, Chlorine, Bromine cannot be the identity of Y?

Fluorine-you got tricked!The answer is a. fluorine.why??? shouldnt the more reactive halogen displace the less reactive ones? heres why. from question 7, you know that fluorine is the most powerful oxidising agent of all halogens. in fact, f is so reactive that it oxidises water in the solution to give hf and oxygen, even before it reacts with other halides in the solution! (the reason being water is in large abundance compared to the halide ions, hence the chance of attacking h2o is much greater and all fluorine will be used up before it gets to react with a significant amount of halide ions) hence, fluorine does not participate in displacement reactions of halides. remember this exception!