The correct answer is invalid.
The statement says: It is false that no jailhouse informants are people who can be trusted. Therefore, some jailhouse informants are not people who can be trusted.
So to solve this we used the Traditional Square of Opposition to resolve the inference and see if it's valid or not. Let's remember that the Traditional Square of Opposition helps us to show the opposition lines or its arrangement to see the logically necessary relations between the categorical propositions that are the Contradictory, opposite truth value. Contrary, one is false. Sub contrary, one is true. And Sub alternation, when falsity flows upwards and truth flows downwards.