**Core Concept**
The first change in a dead body is a post-mortem alteration that occurs due to the breakdown of cellular hemoglobin and the subsequent interaction with oxygen, leading to a characteristic discoloration of the skin.

**Why the Correct Answer is Right**
The correct answer, greenish discoloration of the right iliac fossa (RIF), is a result of the post-mortem process known as algor mortis, where the body's temperature cools. However, the more relevant process here is the breakdown of cellular hemoglobin, which releases free hemoglobin into the tissues. This free hemoglobin reacts with oxygen to form methemoglobin, which has a greenish color. The RIF is often the first area to exhibit this discoloration due to its proximity to the gastrointestinal tract, where bacteria can start breaking down the body's tissues. This process is known as livor mortis or hypostasis.

**Why Each Wrong Option is Incorrect**
**Option A:** Mummification is a process that occurs in hot and dry environments, leading to the desiccation of the body. It is not the first change that occurs in a dead body.
**Option C:** Putrefaction is the process of bacterial decomposition of the body's tissues, which occurs after livor mortis. It is a later stage of post-mortem change.
**Option D:** Maggot formation is a sign of active decomposition, which occurs after putrefaction has begun. It is not the first change that occurs in a dead body.

**Clinical Pearl / High-Yield Fact**
Livor mortis typically occurs within 2-4 hours of death and is a key indicator of the time since death. It is essential to note that the position of livor mortis can be influenced by gravity and the body's position at the time of death.

✓ Correct Answer: B. Greenish discolouration of RIF