**Core Concept**
The patient's presentation of painless lymph node enlargement, fever, weight loss, and anemia, along with the histological features of lymph node biopsy, is suggestive of a type of non-Hodgkin lymphoma (NHL) characterized by a specific nuclear morphology.

**Why the Correct Answer is Right**
The lymph node biopsy findings, with cells having a delicate multilobed, puffy nucleus resembling popped corn, are characteristic of follicular lymphoma. Follicular lymphoma is a type of NHL that arises from the germinal centers of lymphoid follicles. The presence of these distinctive "popped corn" nuclei, also known as "cleaved" or "centrocytic" morphology, is a hallmark of follicular lymphoma. This type of lymphoma often expresses B-cell markers, such as CD20, and typically harbors a specific translocation involving the BCL2 gene, leading to its overexpression and contributing to the pathogenesis of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Burkitt lymphoma, another type of NHL, typically presents with a more aggressive clinical course and characteristic "starry sky" histology, with numerous mitotic figures and apoptotic cells, which is not described in the patient's biopsy.

**Option B:** This option is incorrect because Diffuse large B-cell lymphoma (DLBCL) is a more aggressive type of NHL that often presents with a rapid onset of symptoms and a more pronounced lymphadenopathy, which is not consistent with the patient's 6-month history of symptoms.

**Option C:** This option is incorrect because Mantle cell lymphoma is a distinct type of NHL that typically presents with lymphadenopathy and splenomegaly, but it is characterized by a different histological appearance and often expresses specific markers, such as SOX11.

**Option D:** This option is incorrect because Chronic lymphocytic leukemia (CLL) is a type of lymphoproliferative disorder that typically presents with anemia, thrombocytopenia, and lymphocytosis, but it is characterized by a different histological appearance and often expresses specific markers, such as CD5.

**Clinical Pearl / High-Yield Fact**
Follicular lymphoma is a type of lymphoma that often presents with a more indolent clinical course, but it can transform into a more aggressive lymphoma, such as diffuse large B-cell lymphoma, which requires prompt recognition and treatment.

**Correct Answer:** D. Follicular lymphoma.