Which crime involves wrongfully threatening another person for gain?

The crime that involves wrongfully threatening another person for gain is extortion. Extortion is characterized by the use of threats—whether to inflict harm, expose information, or undermine a person's reputation—to coerce someone into providing money, property, or services. This crime fundamentally relies on the element of intimidation, where the victim feels compelled to comply with the demand due to fear of negative consequences.

In contrast, theft involves taking someone else's property without their consent but typically does not involve threats or intimidation. Fraud is based on deception to secure unfair or unlawful gain, often through misrepresentation or deceit, but does not necessarily include threatening behavior. Assault involves causing physical harm or placing someone in fear of imminent harm, but it does not typically relate to the unlawful acquisition of gain through threats.

Thus, extortion specifically encapsulates the element of threatening behavior aimed at obtaining something of value, making it the correct answer in the context of the question.