Final answer:
A mineral deficiency affects older leaves when the mineral is mobile within the plant, allowing it to be transported to support new growth, thus showing deficiency signs in the older tissues first. Therefore, the most appropriate correct option is E.
Step-by-step explanation:
A mineral deficiency in plants is more likely to affect older leaves more than younger ones if the mineral is very mobile within the plant. Mobile nutrients are those that can move freely from older parts of the plant to newer growth when there is a shortage. This often includes key macronutrients such as nitrogen, phosphorus, and potassium. When these mobile nutrients are deficient, the plant moves them from the older tissues to the younger tissues to maintain new growth. Hence, the older leaves show symptoms of deficiency first. For instance, a deficiency of nitrogen, which is a component of chlorophyll and proteins, can lead to the yellowing of older leaves while younger leaves remain green. Macronutrients such as magnesium, which is involved in the photosynthetic process, show signs of intervenal chlorosis in older leaves, typically when it is deficient.