Explanation:

The word conclusive means having or likely to have the effect of proving a case or something which cannot be denied.Now if we take a look at the options and their meanings:

Decisive: settling an issue orproducing a definite result.

Ambiguous:open to more than one interpretation or not having one obvious meaning.Something which is not definite.\

Undeniable: cannot be neglected or denied.Something obvious.

Clear: Without any doubt or easy to perceive, understand, or interpret.

Hence after looking at the meanings we can definitely conclude that option 2 is the correct answer as other 3 options have similar meaning to the word Conclusive.