Charlie has opted to study both Spanish and French in school this semester. As he studies a list of words for his French test, he realizes that he has forgotten the list of Spanish words he learnt the day before. In the context of retrieval failure, this is an example of

The answer is retroactive interference.

Explanation:

Retroactive interference is a type of retrieval failure in which new information interferes with remembering old information. In this example, learning the French vocabulary made Charlie forget about the Spanish words. This is related to the recency effect, meaning people tend to remember the most recent information the best.

In contrast, proactive interference occurs when old information makes it difficult to acquire new information. This would have happened if Charlie couldn't learn the French words because he confused them with the Spanish vocabulary.