Correct statements among a to d regarding silicones are :
(a) They are polymers with hydrophobic character.
(b) They are biocompatible.
( c ) In general, they have high thermal stability and low dielectric strenght.
(d) Usually, they are resistant to oxidation and used as greases.

Options

A. a,b,c, d
B. a,b and d only
C. a and b only
D. a, b and c only

Explanation

To determine which statements regarding silicones are correct, let's analyze each statement one by one.

### Step 1: Analyze Statement A
**Statement A**: They are polymers with hydrophobic character.

- **Explanation**: Silicones are indeed polymers that possess a hydrophobic character due to the presence of organic groups attached to the silicon-oxygen backbone. This structure makes them repel water, confirming that they are hydrophobic.

**Conclusion**: Statement A is correct.

### Step 2: Analyze Statement B
**Statement B**: They are biocompatible.

- **Explanation**: Silicones are known for their biocompatibility. They are non-irritant and non-toxic, which makes them suitable for medical applications. Their low reactivity further supports their compatibility with biological systems.

**Conclusion**: Statement B is correct.

### Step 3: Analyze Statement C
**Statement C**: In general, they have high thermal stability and low dielectric strength.

- **Explanation**: Silicones are characterized by high thermal stability due to the strong silicon-oxygen bonds, which require a significant amount of energy to break. However, they also exhibit high dielectric strength, making them excellent insulators. Therefore, the statement incorrectly claims low dielectric strength.

**Conclusion**: Statement C is incorrect.

### Step 4: Analyze Statement D
**Statement D**: Usually, they are resistant to oxidation and used as greases.

- **Explanation**: Silicones are indeed resistant to oxidation because they are surrounded by organic groups that provide a protective barrier. This property, along with their lubricating qualities, makes them suitable for use as greases.

**Conclusion**: Statement D is correct.

### Final Conclusion
The correct statements regarding silicones are:
- A: Correct
- B: Correct
- C: Incorrect
- D: Correct

Thus, the correct options are A, B, and D.