Which essential nutrient is indicated by the symbol S?

The symbol S represents sulfur, which is an essential nutrient for plants. Sulfur plays a vital role in the formation of amino acids, proteins, and certain enzymes. It is also crucial for the production of chlorophyll, contributing to photosynthesis, a key process for plant growth and energy production. Additionally, sulfur helps in the synthesis of vitamins and is involved in the overall metabolism of plants.

Understanding sulfur's role helps emphasize why it is important for healthy crop production, as deficiencies can lead to reduced growth, poor crop quality, and lower yields. The other nutrients listed—sodium, silicon, and selenium—while important in specific contexts, do not have the symbol S associated with them and do not serve the same essential roles as sulfur in plant nutrition.