Explanation:

- Culpable means deserving blame or being at fault for something.

- Option 1: Guilty is the most appropriate synonym for culpable. Both imply responsibility for a wrongdoing.

- This is the correct choice.

- Option 2: Irresponsible refers to not showing a proper sense of responsibility, but it's not directly about being at fault in the way culpable is.

- Option 3: Immune means being protected or exempt from something, usually a penalty or obligation, so it’s quite the opposite of culpable.

- Option 4: Innocent means not guilty of a crime or offense, which is the antonym of culpable.

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