The correct answer is (a) Fe.
Maize leaves turn white at the tips due to iron deficiency. This is because iron is essential for the production of chlorophyll, which is the green pigment that gives plants their color. Without chlorophyll, plants cannot photosynthesize, which is the process by which they convert sunlight into energy. As a result, plants with iron deficiency will have pale green or white leaves, and may also be stunted in growth.
Manganese (Mn), nitrogen (N), and zinc (Zn) are also essential nutrients for plants, but they do not typically cause white tips on the leaves. Manganese deficiency can cause interveinal chlorosis, which is a yellowing of the leaves between the veins. Nitrogen deficiency can cause a general yellowing of the leaves, while zinc deficiency can cause a mottled appearance on the leaves.
To prevent iron deficiency in maize, it is important to apply iron-rich fertilizer to the soil. Iron can also be applied as a foliar spray, but this is not as effective as applying it to the soil.