Solution

The organic compounds that make up the body of a plant (carbohydrates such as cellulose and starch, proteins, lipids and nucleic acids) are all built on a carbon skeleton.
Carbon, obtained from atmospheric $CO_2$ through photosynthesis, makes up about 45 percent of the dry weight of a plant, followed by oxygen and hydrogen.
Nitrogen is the most important mineral nutrient taken up from the soil, but its share is only about 1–4 percent of dry weight. Manganese and iron are micronutrients needed in very small amounts.
So the most abundant element present in the plant is carbon.

Concept Carbon in plant dry matter

Mineral Nutrition in past papers

63 questions from this chapter have appeared across 23 exam years.