Which of the following is one of the basic plant nutrients of fertilizers that are commonly used in agriculture?

Potassium

The correct answer is option 4. Potassium.

The basic plant nutrient commonly found in fertilizers used in agriculture is potassium. Potassium is one of the three primary macronutrients essential for plant growth, along with nitrogen and phosphorus. It plays a crucial role in various physiological processes within plants, including photosynthesis, water regulation, and nutrient uptake. Potassium deficiency can lead to stunted growth, reduced crop yield, and increased susceptibility to diseases and pests. Therefore, potassium is a vital component of agricultural fertilizers to ensure optimal plant growth and crop productivity.