When placenta forms a ridge along the ventral structure of the ovary and the ovules are borne on this ridge forming two rows, the type of placentation is termed as
A.Marginal
B.Axile
C.Parietal
D.Free central

Hint: Placentation is defined as the attachment of ovules inside the ovary which is mostly found in flowering plants.

Complete answer:
Different types of placentation are found in different plants. They can be categorized as- basal placentation, parietal placentation, marginal placentation, free central placentation and axile placentation. In basal placentation the placenta is present at the base of the ovary and only a single ovule is attached to it. Examples include marigold and sunflower. In parietal placentation the ovary is one chambered, but it turns into two chambered due to the formation of a false septum, the ovules either form on the inner part or peripheral part of the ovary. Examples include mustard. In marginal placentation the placenta forms a ridge along the ventral structure of the ovary and the ovules are found to be borne on the ridge leading to the formation of two rows. Examples include pea plants. In free central placentation septa is absent and ovules are formed on the central axis. Examples include primrose. In axile placentation the placenta is axial and the ovules are attached in a multilocular ovary. Examples include tomato and orange.

Hence, the correct answer is option (A)

Note: Placenta is an important organ found in flowering plants since it provides the attachment of ovules to the ovary. These ovules after fertilization turn into seeds while the ovary turns into the mature fruit.