**Core Concept**
The staging of oral cancer, including tongue carcinoma, is based on the size and extent of the primary tumor, lymph node involvement, and distant metastasis. The **TNM staging system** is used, where T describes the primary tumor, N describes lymph node involvement, and M describes distant metastasis.

**Why the Correct Answer is Right**
Given the patient has carcinoma of the right tongue on its lateral border of the anterior 2/3rd with a lymph node of size 4 cm in level 3 on the left side of the neck, this indicates **contralateral lymph node involvement**, which is a significant factor in staging. The size of the primary tumor and the presence of a lymph node larger than 3 cm on the opposite side of the neck are critical for determining the stage.

**Why Each Wrong Option is Incorrect**
**Option A:** This would be incorrect because it does not account for the size and location of the lymph node involvement.
**Option B:** This option is incorrect as it likely underestimates the extent of disease given the size and contralateral location of the lymph node.
**Option C:** This is not the correct stage given the information about the primary tumor and the lymph node.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **contralateral lymph node involvement** in head and neck cancers often signifies a more advanced stage of disease, reflecting the tumor's ability to metastasize across the midline.

**Correct Answer:** D. Stage IVC