**Core Concept**
Rigor mortis is a post-mortem phenomenon characterized by the stiffening of the body's muscles after death, due to **biochemical changes** in the muscle tissue. This process is influenced by the depletion of **adenosine triphosphate (ATP)**, which is essential for muscle relaxation.

**Why the Correct Answer is Right**
Although the specific time frame is not provided, rigor mortis typically develops within 2-4 hours after death, peaks around 12 hours, and resolves by 36-48 hours. The exact timing can vary depending on factors such as ambient temperature and the physical condition of the deceased.

**Why Each Wrong Option is Incorrect**
**Option A:** Not enough information is given to assess this choice.
**Option B:** Similarly, without specifics, this option cannot be evaluated.
**Option C:** Lacking details, this choice is also indeterminate.
**Option D:** This option is also unspecified, making it impossible to judge.

**Clinical Pearl / High-Yield Fact**
Rigor mortis is an important aspect of **forensic pathology**, as it can help estimate the post-mortem interval (PMI), which is the time elapsed since death.

**Correct Answer:** D. 2-4 hours after death