**Core Concept**
The question is testing the understanding of ovarian tumor spread and grading according to the FIGO (International Federation of Gynecology and Obstetrics) staging system. The correct answer requires knowledge of the specific criteria for grading ovarian tumors, particularly in the context of tumor seeding on the abdominal surface.

**Why the Correct Answer is Right**
Tumor seeding on the abdominal surface is a characteristic feature of advanced ovarian tumors. In the context of a true pelvis-confined tumor with negative nodes, this finding is indicative of a high-grade tumor. According to the FIGO staging system, tumor seeding on the abdominal surface is classified as T4b, which is a feature of high-grade tumors. Therefore, the correct grading would be a high-grade tumor, specifically Grade 3.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the grading criteria for ovarian tumors with abdominal surface seeding. Grade 1 tumors are typically low-grade and would not be expected to exhibit such aggressive behavior.

**Option B:** This option is incorrect because it does not account for the presence of abdominal surface seeding. Grade 2 tumors may exhibit some degree of aggressiveness, but the presence of tumor seeding would typically indicate a higher grade.

**Option C:** This option is incorrect because it does not accurately reflect the grading criteria for ovarian tumors with abdominal surface seeding. Grade 4 tumors are typically associated with distant metastasis, which is not indicated in this scenario.

**Clinical Pearl / High-Yield Fact**
When evaluating ovarian tumors, it is essential to consider the FIGO staging system and the specific grading criteria for each tumor type. Tumor seeding on the abdominal surface is a red flag for high-grade tumors and requires prompt evaluation and management.

**Correct Answer: C. Grade 3**