The correct answer is option 1: Iron.

Fertilizers are substances that are applied to soil or plants to provide essential nutrients that may be lacking. These nutrients are important for the growth and development of crops. While fertilizers can provide many essential nutrients, they do not typically contain all of them.

Option 2: Potassium is commonly found in fertilizers. It is an essential macronutrient required by all crops for proper growth and development.

Option 3: Nitrogen is also frequently found in fertilizers. It is essential for plant growth, as it is a major component of proteins, enzymes, and chlorophyll.

Option 4: Phosphorus is another nutrient commonly found in fertilizers. It plays a vital role in energy transfer, photosynthesis, and root development.

Alert - correct answer should be Option 1: Iron. Iron is an essential micronutrient required by plants, but it is not typically included in fertilizers. Iron deficiencies can occur in plants, resulting in yellowing of leaves (chlorosis) and reduced growth. In such cases, iron fertilizers or soil amendments may be necessary to correct the deficiency.