The correct answer is: 2.5%.
The camber of a road is the upward slope of the road from the center to the edges. It is designed to help water drain off the road and to prevent hydroplaning. The camber for hill roads is typically higher than for flat roads, as this helps to prevent water from collecting in the center of the road.
A camber of 2.5% is the most common camber for hill roads. This camber provides a good balance between drainage and safety. A camber that is too high can make the road feel unstable, while a camber that is too low can cause water to collect in the center of the road.
The other options are incorrect because they are not the most common camber for hill roads. A camber of 2% is a common camber for flat roads, while a camber of 3% and 4% are more common for highways.