Step 1: Concept
Wheel slip occurs when the actual distance traveled by a tractor is less than the distance it would travel based on the theoretical rotation of its wheels.
Step 2: Meaning
It is a measure of power loss due to the tires spinning on the soil surface without moving the vehicle forward.
Step 3: Analysis
The formula involves comparing the distance covered with no load (zero slip) to the distance covered under a specific draft load.
Step 4: Conclusion
This specific ratio defines the percentage of wheel slip.
Final Answer: (C)