Concept: This question tests your understanding of different types of placentation, which refers to the arrangement of ovules within the ovary.

Why (D) is correct: In marginal placentation, the ovary is typically monocarpellary (formed from a single carpel). The ovules are borne on the ridge along the ventral suture (the fused margins) of the ovary, forming a single row. This is characteristic of legumes like peas.

Why other options are wrong:

• (A) Axile placentation: Occurs in multicarpellary, syncarpous ovaries where ovules are borne on a central axis in locules (e.g., tomato, lemon).
• (B) Parietal placentation: Occurs in multicarpellary, syncarpous ovaries where ovules develop on the inner wall of the ovary, often forming a false septum (e.g., mustard, argemone).
• (C) Free central placentation: Occurs in multicarpellary, syncarpous ovaries where ovules are borne on a central axis, but the septa are absent (e.g., Dianthus, Primrose).

NEET Tip: Remember that marginal placentation is the simplest type and is found in monocarpellary ovaries, often with a single row of ovules along the fused margin.

Correct Answer: (D)