**Core Concept**
The patient's presentation of primary infertility and a palpable pelvic mass, combined with a normal CA-125 level, suggests a condition that affects ovarian function and can lead to pelvic masses. This scenario is likely related to a disorder of ovarian development.

**Why the Correct Answer is Right**
The patient's symptoms and normal CA-125 level are consistent with a diagnosis of **Müllerian duct anomalies**, specifically a **Müllerian agenesis**. This condition occurs when the Müllerian ducts fail to develop properly during embryogenesis, leading to the absence or underdevelopment of the upper portion of the vagina and uterus. Müllerian agenesis is often associated with primary infertility due to the absence of a functional uterus.

In contrast, **Option A**, **Egg Yolk Cyst**, is a type of ovarian cyst but would not usually present with a palpable pelvic mass and primary infertility as the primary symptoms. **Option B**, **Dermoid Cyst**, is another type of ovarian cyst but is not typically associated with Müllerian duct anomalies. **Option C**, **Endometrioma**, is a type of ovarian cyst associated with endometriosis, which is not supported by the patient's normal CA-125 level.

**Why Each Wrong Option is Incorrect**
* **Option A:** Egg Yolk Cyst is a type of ovarian cyst that can cause pelvic pain and discomfort but is not typically associated with primary infertility and Müllerian duct anomalies.
* **Option B:** Dermoid Cyst is a type of ovarian cyst that can cause pelvic pain and discomfort but is not typically associated with Müllerian duct anomalies and primary infertility.
* **Option C:** Endometrioma is a type of ovarian cyst associated with endometriosis, which is not supported by the patient's normal CA-125 level.

**Clinical Pearl / High-Yield Fact**
Müllerian agenesis is a rare congenital disorder that affects the development of the female reproductive system. It is often associated with primary infertility and other reproductive issues.

**Correct Answer:** C. Müllerian agenesis.