The correct option is A Copper.
Copper is an important micronutrient which involves in the lignification of plant and also provides standibility to the plants. It is the main component of protein and enzyme that regulates the metabolic activities ion plants. Its deficiency can reduce the lignification which turns leaves of citrus plant wilt, brown colour and even dies. This condition is called as die back of citrus. It also stops the seed maturity and causes chlorosis. This condition is called as reclamation of legumes and cereals.