Okay, let's tackle this question. The scenario is about an intern who was reprimanded for not sending blood samples and later yelled at a family member about changing a normal saline drip. The question is asking about the defense mechanism the intern is using.

First, I need to recall different psychological defense mechanisms. Common ones include denial, projection, rationalization, displacement, reaction formation, etc. The key here is to figure out which one fits the situation.

The intern was criticized for a mistake (forgetting to send blood samples). Later, he yells at a family member over changing a drip. This seems like redirecting his frustration from the real issue (his mistake) to something else (the family member). That sounds like displacement, where someone redirects emotions from the original source to a safer target.

Projection would be if he blamed others for his mistake. Reaction formation might be if he acted opposite to his true feelings, but that doesn't fit here. Rationalization would be making excuses for his mistake, which isn't exactly what's happening. Displacement is the best fit here because he's taking out his anger from being reprimanded onto the family member about a different issue.

Now, checking the options. The correct answer should be displacement. The other options don't fit the scenario. The clinical pearl would be to remember that displacement involves redirecting emotions to a less threatening target, which is a common exam question point.

**Core Concept**
This question tests understanding of psychological defense mechanisms, specifically **displacement**, a key concept in psychodynamics. Displacement involves redirecting emotions from the original source to a safer or more acceptable target, often to avoid direct conflict or anxiety.

**Why the Correct Answer is Right**
The intern redirects his frustration from being reprimanded (the real issue) onto an unrelated situation (the family member’s request about the saline drip). This is classic **displacement**—transferring emotional energy from a threatening stimulus (senior’s criticism) to a less threatening one (the family member). The mechanism protects the intern from confronting his guilt or anxiety directly.

**Why Each Wrong Option is Incorrect**
**Option A:** *Projection* involves attributing one’s own unacceptable feelings to others (e.g., accusing others of being critical). This does not fit the scenario.
**Option B:** *Reaction formation* involves behaving opposite to one’s true feelings (e.g., acting overly kind to hide hostility). The intern’s behavior does not align with this.
**Option C:** *Rationalization* justifies actions with logical explanations (e.g., blaming the family for the forgotten blood samples). The intern’s outburst lacks this cognitive justification.

**Clinical Pearl / High-Yield Fact**
Remember **"Displacement = Redirecting emotion from A to B"** (e.g., yelling at a spouse after a bad day at work). NEET/USMLE questions often test this alongside projection and reaction formation. Focus on the *shift in target* of the emotional response.

**Correct Answer: D. Displacement**

✓ Correct Answer: A. Displacement