Answer:
The word that is a coordinating conjunction is "for".
Explanation:
A coordinating conjunction is a word that connects other words, clauses, or sentences that have the same syntactic importance. The conjunctions are: for, and, nor, but, or, yet, and so.
In "Plan ahead, for you never know what problems will arise", we have two independent clauses. Independent clauses are capable of expressing full ideas without the help of other clauses. In this case, they were connected by the coordinating conjunction "for" so that the second clause expresses the reason for the first one. The reason why you should plan ahead is that fact that you never know what problems will arise.
