**Core Concept**
Randomization is a fundamental principle in research and clinical trials, ensuring that participants are allocated to treatment or control groups in a way that minimizes bias. This is crucial for establishing cause-and-effect relationships between interventions and outcomes.

**Why the Correct Answer is Right**
Randomization implies that each participant has an equal chance of being assigned to any group, thereby reducing selection bias. This is known as a randomization scheme with equal probability. The allocation of participants is also known to the researcher, allowing for accurate tracking and analysis. Randomization with equal and known chances is essential for obtaining reliable and generalizable results.

**Why Each Wrong Option is Incorrect**
**Option A:** Unequal and known chances are not possible in a true randomization scheme, as this would introduce bias and undermine the validity of the study.

**Option C:** Unequal and unknown chances contradict the principles of randomization, which aims to eliminate bias and ensure equal probabilities of assignment.

**Option D:** Equal but unknown chances may seem plausible, but in practice, it is challenging to maintain the integrity of the randomization process without knowing the allocation sequence.

**Clinical Pearl / High-Yield Fact**
In clinical research, randomization should be implemented using a secure and tamper-proof method to prevent selection bias and ensure the integrity of the study results.

**✓ Correct Answer: B. Equal and known chances**