Explanation:

- Confront: To face or deal with a difficult situation or challenge directly. It implies a direct approach to an issue, often involving an element of bravery or assertiveness.

- Mingle (Option 1): To mix or combine, especially in social contexts. It’s about being sociable rather than dealing with challenges.

- Conceal (Option 2): To hide or keep something secret. It's the opposite of confronting since it involves hiding rather than facing something openly.

- Challenge (Option 3): To call upon someone to engage in a contest or to question the validity of something. It fits well with the idea of confronting as it involves direct engagement and opposition.

- Scheme (Option 4): To plan or arrange especially in a secret way, usually with negative connotations. Does not relate to directly facing a problem.

The correct synonym for "Confront" is Option 3: Challenge.

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