Okay, let me tackle this question. The question is asking about the first external sign of decomposition in a dead body. Hmm, decomposition processes... So, I need to recall the stages of decomposition. Let me think.

First, after death, the body goes through several stages. The initial signs would be related to the breakdown of cells. Rigor mortis comes early, but that's an internal change. Then there's algor mortis, cooling, but that's also internal. Wait, the first external sign... Maybe it's something visible on the skin.

Oh, right! Livor mortis, or postmortem lividity, is the settling of blood in the dependent parts of the body. But that's an external sign. But wait, when does that start? It begins within minutes to an hour after death. But is that considered the first external sign? Or is there something else?

Wait, there's also putrefaction. The first visible signs of putrefaction would be in the abdomen, maybe. Because the bacteria in the gut start breaking down tissues. So maybe the first external sign is greenish discoloration of the abdomen? That's usually the first sign of decomposition. The green color due to the breakdown of hemoglobin into biliverdin and other pigments.

So the options might be A. Greenish discoloration of abdomen, B. Rigor mortis, C. Postmortem lividity, D. Marbling. Let me check again. Postmortem lividity occurs first, but it's a purplish color in dependent areas. Then after some time, the abdomen starts to show green discoloration due to putrefaction. So the first external sign would be livor mortis, but maybe the question is about decomposition as in putrefaction. Wait, the question says "decomposition" of the dead body. So decomposition here refers to the process of putrefaction. Then the first sign would be the greenish discoloration in the abdomen. So the correct answer would be the greenish discoloration of the abdomen. Let me confirm. Yes, in forensic pathology, the first sign of decomposition is the greenish discoloration starting in the right lower quadrant, where the appendix is. So the answer is option A. Greenish discoloration of the abdomen. The other options: B. Rigor mortis is an internal change, not external. C. Postmortem lividity is an external sign but occurs earlier than decomposition. D. Marbling is a later stage. So the correct answer is A.

**Core Concept**
Decomposition of a dead body begins with autolysis and bacterial activity, leading to visible external changes. The first identifiable sign involves enzymatic breakdown of tissues and bacterial byproducts altering skin color.

**Why the Correct Answer is Right**
The first external sign is **greenish discoloration of the abdomen**, caused by putrefactive bacteria breaking down hemoglobin into biliverdin. These bacteria proliferate in the gut, spreading via lymphatics to abdominal walls. This typically starts in the right lower quadrant (near the appendix) within 24–48 hours postmortem.

**Why Each Wrong Option is Incorrect**
**Option B:** *Rigor mortis* is an internal biochemical change (muscle stiffening) and not externally visible.
**Option C:** *Post

✓ Correct Answer: B. Greenish discoloration over right iliac fossa