**Core Concept**
The pelvis is a key anatomical region for sex determination due to its distinct differences in shape and size between males and females. These differences are primarily attributed to the wider pelvic outlet and larger pelvic dimensions in females, which facilitate childbirth.

**Why the Correct Answer is Right**
The pelvis is the most reliable bone for sex determination in forensic medicine because of its unique features. The pelvic brim is wider in females, and the subpubic angle is more obtuse (around 90-100°) compared to males (around 60-70°). Additionally, the pre-auricular sulcus, ischial tuberosity, and greater sciatic notch are also more pronounced in females. These differences allow for accurate sex determination in most cases.

**Why Each Wrong Option is Incorrect**
* **Option A:** The skull is not a reliable bone for sex determination due to overlapping features between males and females. Although some studies suggest that the skull can be used for sex determination, it is not as accurate as the pelvis.
* **Option C:** The femur, while useful for estimating stature, does not exhibit significant sex-specific differences that would make it a reliable bone for sex determination.
* **Option D:** The tibia and fibula are not suitable for sex determination due to their lack of distinct sex-specific features.

**Clinical Pearl / High-Yield Fact**
When examining the pelvis for sex determination, it's essential to consider the overall shape and size, rather than relying on individual features. A combination of the subpubic angle, pre-auricular sulcus, ischial tuberosity, and greater sciatic notch can provide a more accurate assessment of sex.

✓ Correct Answer: B. Pelvis