Characteristics of Maize:
- C3 pathway: Maize follows the C3 pathway of photosynthesis. In this pathway, the first stable product formed during photosynthesis is a three-carbon compound called 3-phosphoglyceric acid (PGA). This pathway is less efficient in terms of carbon fixation compared to the C4 pathway, which is followed by plants like sugarcane and corn.
- Closed vascular bundles: Maize has closed vascular bundles, which means that the xylem and phloem are surrounded by a layer of cells called bundle sheath cells. This arrangement provides mechanical support and protection to the vascular tissues.
- Scutellum: The scutellum is a specialized structure found in the embryo of maize seeds. It is a modified cotyledon that stores nutrients and plays a crucial role in the germination and early growth of the seedling.

Explanation of the Correct Answer:
The correct answer is option 'B', which corresponds to the characteristics of Maize. Let's analyze the given options and their characteristics:

a) Onion: The characteristics mentioned for onion are bulb, imbricate aestivation, and axile placentation. A bulb is a modified underground stem consisting of fleshy storage leaves. Imbricate aestivation refers to the overlapping arrangement of sepals or petals in a floral bud. Axile placentation indicates that the ovules are attached to the central axis of the ovary. None of these characteristics match with maize.

b) Maize: As discussed above, maize exhibits the characteristics of the C3 pathway, closed vascular bundles, and scutellum. These characteristics are specific to maize and accurately describe its features.

c) Tomato: The mentioned characteristics for tomato are twisted aestivation, axile placentation, and berry. Twisted aestivation refers to the arrangement of sepals or petals in a floral bud where one margin overlaps the adjacent margin and the other margin is overlapped by the adjacent one. Axile placentation indicates that the ovules are attached to the central axis of the ovary. A berry is a fleshy fruit derived from a single ovary. These characteristics do not match with maize.

d) Pea: The given characteristics for pea are C3 pathway, endospermic seed, and vexillary aestivation. Vexillary aestivation refers to the arrangement of sepals or petals in a floral bud where the largest sepal or petal overlaps the two adjacent ones, and the two smaller ones are enclosed within. The C3 pathway is mentioned for pea as well, but maize is a better fit for this characteristic. Endospermic seed means that the seed has a well-developed endosperm, which is a storage tissue in the seed. In maize, the scutellum plays a similar role. Therefore, the characteristics mentioned for pea do not match with maize.

Hence, the correct answer is option 'B' which represents the characteristics of Maize.