Final answer:
Chlorosis was historically cured by the micronutrient iron (Fe).
Step-by-step explanation:
Chlorosis is a condition in which plants exhibit yellowing of leaves due to insufficient chlorophyll production. One of the micronutrients historically noted to cure chlorosis is iron (Fe). Iron is an essential component of the chlorophyll molecule, and its deficiency can lead to impaired photosynthesis and chlorosis in plants. Providing iron as a chelate complex or water-soluble salt can help alleviate chlorosis and restore normal leaf coloration.