Which of the following words is spelled correctly?

"Similarly" is used to indicate that something is done in a similar manner or order to what was just mentioned, which implies a sequence or continuation of ideas.

Similarly is a transitional expression that is used to show sequence.

The prefix "inter-" implies involvement or connection between different entities.

The suffix "-ness" is used to create abstract nouns from adjectives, indicating the quality or condition of being well. In this case, "wellness" refers to the state of being in good health or well-being.

The word "crucial" is the only correct spelling and fits the context of the sentence.

The prefix "ir-" (meaning "not") combined with the suffix "-ible" (meaning "able to be") forms the word "irresistible," which describes something that is too enticing or powerful to be resisted.

This sentence uses a casual, conversational tone and an informal comparison ("middle school sleepover") that does not suit a formal or professional context, making it informal.

The word "she" agrees with "a person," which is a singular antecedent.

The prefix that implies duplication when attached to a root word is "re-." For example, "redo" means to do again, indicating duplication of the action.