Which pesticide formulation represents the highest concentration?

The formulation that represents the highest concentration is 4 EC. The "EC" designation stands for "emulsifiable concentrate," which typically contains a high percentage of active ingredient dissolved in a solvent. Emulsifiable concentrates generally have a higher concentration of active ingredient compared to other formulations, making them more potent in a smaller volume.

In contrast, the other options represent formulations with varying concentrations. For example, "WP" stands for "wettable powder," which usually involves a lower concentration because it needs to be suspended in water for application. Similarly, "D" in 15D denotes a dilution ratio that implies the formulation is more diluted than an emulsifiable concentrate. The "G" in 5G signifies a granular formulation, which also tends to have lower concentrations compared to liquids because granules often contain carriers along with the active ingredient.

Thus, given the nature of these formulations, 4 EC is the one with the highest concentration of active ingredient, making it correct in this context.