Which of the following processes occurs in green plants during the day?

In green plants during the day, both respiration and photosynthesis are occurring simultaneously.

Photosynthesis is the process by which plants, using chlorophyll in their chloroplasts, convert light energy from the sun into chemical energy in the form of glucose. This process requires sunlight, carbon dioxide, and water, and produces oxygen as a byproduct. Therefore, during the daytime, when light is available, photosynthesis is actively taking place.

At the same time, respiration is a process that occurs in all living cells, including those in plants. During respiration, glucose is broken down with the help of oxygen to release energy, which is vital for the plant's growth and maintenance. While the rate of respiration in plants is relatively constant, it does not cease during the day; it continues alongside photosynthesis.

Transpiration, on the other hand, is the process of water vapor loss from the plant's leaves. Though this also occurs during the day and is related to photosynthesis, it is not a metabolic process in the same sense as photosynthesis and respiration.

Therefore, during the day, both photosynthesis and respiration occur in green plants, leading to the correct answer of both processes being involved.