Step 1: Understanding the Concept:
Defense mechanisms are unconscious psychological strategies used by the ego to protect itself from anxiety arising from unacceptable thoughts or failures.
Step 2: Detailed Explanation:
Rationalization involves creating socially acceptable or logical reasons for behavior that is actually driven by different, less acceptable motives.
Rohan is making excuses (biased teacher, unfair exam) to avoid the painful reality of his own lack of preparation.
Repression is pushing unpleasant thoughts into the unconscious.
Projection is attributing one's own unacceptable traits to others (e.g., if Rohan was biased and called the teacher biased).
Denial is the total refusal to accept that an event occurred (e.g., Rohan saying he didn't fail).
Because Rohan is providing "logical" sounding excuses for his failure, it is Rationalization.
Step 3: Final Answer:
Rohan is using the defense mechanism of Rationalization.