Why is wet chalk not visible on blackboard but is visible when it dries?

Wet chalk on a blackboard appears less visible because the moisture creates a smooth layer that reflects light differently than the rough, dry chalk. When chalk is wet, it can also become translucent, allowing the blackboard's color to show through. As the chalk dries, it returns to a solid state with a rough texture that scatters light, making the markings more visible against the dark background.