Final answer:
Nitrogen fixation is the process by which atmospheric nitrogen is converted into an inorganic compound, such as ammonia, which plants can easily utilize.
Step-by-step explanation:
Process Producing Inorganic Compounds for Plants
The process which produces an inorganic compound that plants can easily use is nitrogen fixation (option b). Nitrogen fixation is a biological process by which nitrogen (N2) in the atmosphere is converted into ammonia (NH3) or related nitrogenous compounds in soil and water. These inorganic compounds are readily absorbed by plants and used to synthesize essential molecules such as amino acids, proteins, and nucleic acids.
While photosynthesis (option a) is crucial for converting carbon dioxide and water into carbohydrates and oxygen using sunlight, it does not produce inorganic nitrogen compounds that plants need. Cellular respiration (option b) is a process used by all organisms, including plants, to convert carbohydrates into energy, releasing carbon dioxide and water in the process. Photosystem II (option c) is part of the light reactions in photosynthesis and is not directly involved in nitrogen fixation.