The correct answer is Option 4: NPK.

NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K), which are the three primary macronutrients essential for plant growth. NPK fertilizers are mixed fertilizers that contain varying ratios of these three nutrients. They are commonly used in agriculture and gardening to provide plants with the necessary nutrients for healthy growth.

Let`s break down the reasoning behind this choice:

1. Option 1: CAM

CAM (Crassulacean Acid Metabolism) is a type of photosynthesis pathway used by certain plants in arid conditions. It is not a fertilizer but a biological process in plants.

2. Option 2: Urea

Urea is a commonly used nitrogenous fertilizer. It is a synthetic organic compound that contains a high concentration of nitrogen. However, it is not considered a mixed fertilizer because it only provides nitrogen and lacks the other essential nutrients like phosphorus and potassium.

3. Option 3: Ammonium Sulphate

Ammonium Sulphate is another nitrogen-based fertilizer that contains both nitrogen and sulfur. Similar to urea, it does not contain the complete set of essential nutrients required for balanced plant nutrition.

4. Option 4: NPK

NPK fertilizers are composed of a blend of nitrogen, phosphorus, and potassium in varying ratios. These fertilizers are formulated to provide plants with a balanced nutrient supply, as all three nutrients play critical roles in different aspects of plant development. Nitrogen promotes leaf and stem growth, phosphorus supports root development and flowering, while potassium enhances overall plant health and resistance to diseases.

It is important to note that different plants have specific nutrient requirements, and the choice of fertilizer should be based on the specific needs of the plants being cultivated. However, NPK fertilizers are widely used and provide a comprehensive nutrient mix for many types of plants, making them a popular choice in agriculture and gardening practices.

In summary, NPK is considered a mixed fertilizer because it contains a combination of nitrogen, phosphorus, and potassium, which are all essential nutrients for plant growth and development.