Step 1: Concept
There are four fundamental forces in nature: Gravitational, Electromagnetic, Weak Nuclear, and Strong Nuclear forces.
Step 2: Meaning
Relative strength is measured by comparing how powerful these forces are at the subatomic or macroscopic level.
Step 3: Analysis
Gravitational force is the weakest. Weak Nuclear force is stronger than gravity but weaker than the others. Electromagnetic force is very strong, but the Strong Nuclear force, which binds protons and neutrons in a nucleus, is the most powerful of all.
Step 4: Conclusion
The Strong Nuclear force is approximately 100 times stronger than the electromagnetic force and $10^{38}$ times stronger than gravity.
Final Answer: (D)