In a micelle, which part faces outward toward water?

The correct option is Ionic head.

To understand why this is correct, let's look at the structure and behavior of surfactant molecules (like soap or detergent) in water:
1. Amphiphilic Nature: Surfactant molecules have two distinct parts: a polar/ionic hydrophilic (water-loving) head and a non-polar hydrophobic (water-fearing) hydrocarbon tail.
2. Micelle Formation: When these molecules are dispersed in water above a certain concentration, they aggregate to form spherical structures called micelles. This organization minimizes the free energy of the system.
3. Spatial Orientation: To shield the water-fearing hydrophobic hydrocarbon tails from the water, the tails cluster together in the interior of the micelle. Conversely, the water-loving hydrophilic ionic heads point outward, facing the surrounding water. This favorable interaction stabilizes the micelle in an aqueous environment.