"Converse," when used as a verb, means to engage in conversation, or to "talk." When used as an adjective, "converse" means opposite, but since all of the potential answer choices are verbs, this should not be the meaning of "converse" that we rely upon.

To "castigate" is to criticize.

"Obfuscate" means to make something unclear or confusing. It can also mean to hide. "Hide" is the best choice as it is part of the definition of "obfuscate." Considering the other answer choices, "reveal" means to make known or to show, "obtuse" means not smart or dull, "complain" means to express dissatisfaction, and "complex" means complicated.  

"To underscore" is to emphasize or to stress.

To "digress" means to veer off from a topic, specifically in speech. (Example: "Jonathan has trouble staying on point and often digresses when offering explanations.") Thus, "wander" is closest in meaning to "digress" and is therefore the synonym.

To "prattle" means to talk on and on in a manner that is silly and senseless. To "babble" means to speak in a way that is illogical and unintelligent sounding. Given how similar these words are, they are synonyms. While it may "annoy" someone to hear another person "prattle," the words are not synonyms because they don't mean the same thing. (Instead, there is a causal relationship between them: when one person prattles, that can annoy another.)

"Debunk" means to prove to be false. While the word sounds like it might mean to "untuck," this answer choice is a trick. The best answer choice is thus "disprove," which means to prove that something is not true.

"Indemnify" is a verb that means to compensate someone for a damage or loss.  It can also mean to ensure financial reimbursement in case of a future loss.  The root word "indemnis" means unhurt. So, "compensate" is the correct answer because it is the answer choice closest in meaning to "indemnify."

"Decree" can function either as a noun or an verb. As a noun, a "decree" is a law or rule made by an authority; as an verb, it means to create such a law or rule and put it into effect. While "imperial" may seem like a good answer choice because someone who is imperial may issue decrees, "imperial" is not a synonym of "decree," so we should skip it. Of the listed answer choices, "command" is the closest synonym; it can similarly act as a noun or verb and means either an order issued by an authority or to issue such an order.

"Corroborate" is a verb which means "confirm or give support to a statement, theory, or finding," so we need to find another verb which means "confirm." While "acclaim" might seem like the correct answer, it actually means "praise enthusiastically and publicly," and doesn't quite match the meaning of "confirm" that we're looking for. "Validate," on the other hand, means "check or prove the validity or accuracy of something," and since it is the closest in meaning to "corroborate," it is the correct answer.