What is the main difference between organic and inorganic fertilizers?

The main difference between organic and inorganic fertilizers lies in their origin. Organic fertilizers are derived from natural sources - decomposed plant matter, animal manure, compost, bone meal, fish meal, and other biological materials. Inorganic (mineral or synthetic) fertilizers are manufactured through industrial chemical processes, such as the Haber-Bosch process for producing ammonium-based nitrogen fertilizers or the treatment of phosphate rock with acid to produce superphosphate.

The other options contain inaccuracies:

• Inorganic fertilizers are generally more polluting than organic fertilizers, not less. They are a major source of water pollution (eutrophication) and can degrade soil structure over time with excessive use.
• Organic fertilizers are not necessarily more readily available than inorganic fertilizers. In fact, inorganic fertilizers are often easier to obtain commercially, especially in urban areas.
• The claim that organic fertilizers provide only micronutrients while inorganic fertilizers provide only macronutrients is incorrect. Organic fertilizers supply both macro- and micronutrients (albeit in lower, slower-release concentrations), and inorganic fertilizers can be formulated to include micronutrients as well.