Explanation:

- In the sentence, "I accidentally let the cat out of the bag about your promotion," the idiom "let the cat out of the bag" is used.

- Option 1: "To state the wrong facts" – This means providing incorrect information, but it doesn't relate to revealing a secret.

- Option 2: "To reveal a secret" – This is the correct meaning. The idiom is used when someone accidentally reveals something that was meant to be kept confidential.

- Option 3: "To say something unrealistic" – This implies saying something impractical or fanciful, unrelated to secrets.

- Option 4: "To discourage someone" – This is about making someone lose hope or confidence, which is not relevant here.

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