Which of the following is not a property of silicones ?

Options

A. They are combustible
B. They are water-repellant
C. They are polymeric liquids or solids
D. They have low thermal conductivity.

Explanation

To solve the question "Which of the following is not a property of silicones?", we will analyze the properties of silicones provided in the options.

### Step-by-Step Solution:

1. **Identify the Properties of Silicones:**
- Silicones are known for several key properties, including their thermal stability, water repellency, and polymeric nature.

2. **Evaluate Each Option:**
- **Option 1: Combustibility**
- Silicones are generally considered non-combustible due to their high ignition temperature (around 500 degrees Celsius). Therefore, this statement is false regarding silicones.
- **Option 2: Water Repellent**
- Silicones possess water-repellent properties due to their non-polar alkyl groups in their structure. This statement is true.
- **Option 3: Polymeric Liquids or Solids**
- Silicones exist in complex polymeric forms, which can be either liquids or solids. This statement is also true.
- **Option 4: Low Thermal Conductivity**
- Silicones have low thermal conductivity due to the strong bonds between silicon and oxygen atoms, making this statement true as well.

3. **Conclusion:**
- Among the options evaluated, the only statement that is not a property of silicones is that they are combustible. Therefore, the answer is **Option 1**.

### Final Answer:
**Option 1: Combustible** is not a property of silicones.