Is expelled a transitive or intransitive verb?

This would depend on how the verb is used in the sentence.  A transitive verb  has a direct object.  That means you can answer the question "Who" or "What" is receiving the action.  An intransitive verb has no direct object.  For example, "I walked the dog down the street."  My action verb is "walked".  I can answer who I walked (the dog), so there is a direct object.  Therefore, walked is a transitive verb.  Ask yourself that question as you see how 'expelled' is used in the sentence.