Step 1: Concept
Relentless means oppressively constant, harsh, or inflexible.
Step 2: Meaning
The goal is to find the *opposite* meaning.
Step 3: Analysis
- Merciless is a synonym.
- Yielding (Option b) means giving way under pressure or being flexible, which is the opposite of being relentless.
Step 4: Conclusion
The antonym of relentless is yielding.
Final Answer: (b)