What happens when a collider marked as trigger is touched in Unity?

When a collider is marked as a trigger in Unity, it allows for special collision detection that does not result in a physical reaction between colliding objects. This means that the physics system ignores the standard collision response that would typically occur when two colliders interact, such as bouncing off or stopping each other.

Instead, when a collider marked as a trigger intersects with another collider, it generates a trigger event, which can be used to execute specific behaviors in your game. These behaviors could include activating scripts, changing states, or offering items to a player without applying any physical forces.

This setup is particularly useful for scenarios like collectibles (where the player picks up an item upon contact) or for areas that trigger events (like entering a zone that starts a cutscene or an interaction point). The absence of a physical reaction allows objects to move through the trigger collider without being affected, giving developers the flexibility to design interactions seamlessly.

Thus, the option stating that the physics system ignores the collision is the most accurate representation of what occurs with trigger colliders in Unity.