Which nutrient is essential for chlorophyll synthesis and is mobile within the plant?

Magnesium is essential for chlorophyll synthesis because it is a central component of the chlorophyll molecule, which is crucial for photosynthesis. Without magnesium, plants cannot effectively produce chlorophyll, leading to poor growth and reduced photosynthetic capacity. This nutrient is also classified as mobile within the plant, meaning it can be translocated from older tissues to younger, actively growing tissues. This mobility is important, especially when conditions lead to deficiency, as the plant can redistribute magnesium to maintain chlorophyll production in new growth, thereby sustaining photosynthesis even under low nutrient availability.

In contrast, the other nutrients mentioned do not share these characteristics in the same way. Chlorine, while necessary for certain plant processes, is not involved in chlorophyll synthesis and has limited mobility. Sodium is not classified as an essential nutrient for most plants and is primarily relevant in some specific plant species. Potassium, while important for plant health and function, is not a part of the chlorophyll structure itself. Thus, magnesium stands out as the nutrient that meets both criteria.