RXN #1 and #4 will give you the same product as reactants...so thats out of the question...RXN #3 will does a substiution RXN or even an elimation RXN which will give you two alkene product or a single substitution RXN
so now youre down to RXN 2 and 5...if you can see RXN 2 will give you two products a major and minor product....depending on the hydrogen you want to take...so that leaves us with RXN #5...no matter what hydrogen you take from any of the adjacent carbons it will give you 1 product and 1 product only