8. Yellow spots on citrus leaves is due to the deficiency of:

(A) Zinc
(B) Magnesium
(C) Boron
(D) Iron

Ans: (B) Magnesium

Explanation: Mineral Deficiency in Citrus Leaves - When the citrus tree is not getting the proper nutrients, its leaves can begin to yellow. Nitrogen deficiency shows as light yellow-green leaves with veins slightly lighter than the foliage. New leaves are smaller and thin, and mature leaves begin to develop mottled, irregular yellow blotches. This yellowing can cover entire leaves, which then fall from the branches. When the citrus tree has a magnesium deficiency, yellow irregularly shaped blotches appear at the base of the leaves growing close to the fruit. These blotches will enlarge and eventually cover all but the tip of the leaf. Leaves retaining their greenish color will drop when the tree is water stressed or the weather turns cold. In soil pH levels below 5, use dolomite to raise the pH to between 6.0 and 6.5 and increase the magnesium readily available in the soil. Because each species of citrus tree has its own specific fertilizer balance requirements and soil composition is different, it is best to regularly test the soil with a soil test kit and adjust the nutrient level based on the soil and the citrus’s mineral requirements. (Source: homeguides.sfgate.com/citrus-trees-yellow-leaves-44274.html)