Explanation:

- Principle of Res Judicata: It prevents the same case from being tried again, ensuring finality in litigation.

- Option 1: Mandatory

- Res Judicata is depicted as a mandatory legal principle.

- It must be applied to maintain judicial efficiency and avoid contradictory judgments.

- Good governance and judicial integrity depend on its consistent application.

- Option 2: Directory

- This suggests a guideline, not a compulsion.

- In case of Res Judicata, it cannot just be a suggestion as court decisions rely on it.

- Option 3: Discretionary

- Implies that its application can be based on a judge's choice.

- Res Judicata does not fit this as its consistent application is necessary to avoid legal chaos.

- Option 4: All the above

- Combining all characteristics is impossible for this principle.

- Correct Answer: Option 1 - Mandatory