The inability of a viable seed to germinate due to the lack of favourable external conditions is

Options

A. silence
B. quiescence
C. seed dormancy
D. senescence

Answer

To solve the question regarding the inability of a viable seed to germinate due to the lack of favorable external conditions, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the term that describes a viable seed's inability to germinate when external conditions are not favorable.

2. **Analyzing the Options**:
- **Option 1: Silence** - This term does not relate to seed germination or plant biology. It is incorrect.
- **Option 2: Quiescence** - This refers to a state of suspended growth in seeds, but it is not specifically about the inability to germinate due to external conditions. Thus, it is also incorrect.
- **Option 3: Seed Dormancy** - This term refers to a condition where seeds are viable but do not germinate due to unfavorable environmental conditions. This is the correct answer.
- **Option 4: Senescence** - This term relates to the aging process in plants and is not relevant to seed germination. Therefore, it is incorrect.

3. **Conclusion**: Based on the analysis of the options, the correct answer is **Seed Dormancy** (Option 3).

### Final Answer:
The inability of a viable seed to germinate due to the lack of favorable external conditions is called **Seed Dormancy**.