Which compound is a member of the same homologous series as 1-chloropropane? A. 1-chloropropene B. 1-chlorobutane C. 1-bromopropane D. 1,1-dichloropropane
It's B. Chlorobutane
In explaining this answer, I'd test the students knowledge of what a homologous series is. And then we'd draw out the alternative answers and I'd ask the student to explain why each incorrect answer is incorrect.
Obviously this takes more time than would perhaps be available in an exam- the trick is to get comfortable enough at doing this to be able to ideally do it in your head, or at least with a quick scribble on the exam paper.