The correct answer is option 4: nitrogen, phosphorus, and potassium.

Macro-nutrients are essential for plant growth and development, and inorganic fertilizers are a commonly used source of these nutrients. Carbon, iron, and boron mentioned in option 1 are actually micro-nutrients, required by plants in smaller quantities. Option 2 includes magnesium, manganese, and sulfur, which are also micro-nutrients. Option 3, consisting of magnesium, zinc, and iron, includes both macro and micro-nutrients.

Nitrogen, phosphorus, and potassium are considered macro-nutrients as plants require them in large amounts. Nitrogen is essential for chlorophyll formation and overall plant growth. Phosphorus is important for energy transfer and root development. Potassium helps with water regulation and stresses tolerance in plants. These nutrients are vital for the proper functioning of various plant processes.

Therefore, option 4 correctly identifies the macro-nutrients provided by inorganic fertilizers as nitrogen, phosphorus, and potassium.