Which of the following is essential for plant photosynthesis?

Carbon dioxide is essential for plant photosynthesis as it is one of the primary raw materials plants utilize to produce glucose, a vital source of energy. During this process, plants absorb carbon dioxide from the atmosphere through small openings in their leaves called stomata. The carbon dioxide then combines with water, which plants absorb through their roots, in the presence of sunlight. This chemical reaction, facilitated by chlorophyll in the plant's leaves, results in the production of glucose and oxygen.

In the context of the other options, while oxygen is a crucial byproduct of photosynthesis and nitrogen and hydrogen play significant roles in plant growth and various physiological processes, they are not directly involved in the photosynthesis pathway as carbon dioxide is. Thus, carbon dioxide stands out as the essential component specifically required for this fundamental process of energy production in plants.