Correct statements among 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 strength.
(d) Usually, they are resistant to oxidation and used as greases.

We first recall what a silicone (also called a polysiloxane) is: it is a polymer that possesses a repeating $$\bigl[-\text{Si(R)}_2-\text{O}-\bigr]_n$$ backbone, where each silicon atom is bonded to two organic substituents $$R$$ (most commonly $$\text{CH}_3$$). Because there are no -OH or -NH groups attached directly to the surface of the chain, the exterior of the polymer is almost completely covered with non-polar $$\text{C-H}$$ bonds.

This structural feature makes the entire chain non-polar. A non-polar surface is unable to interact appreciably with water, and therefore silicones repel water. So, they possess a strong water-repelling or hydrophobic character. Hence statement (a) “They are polymers with hydrophobic character” is true.

Next, we look at the interaction of silicones with living tissue. Since they are chemically inert, do not release toxic ions, and are flexible, silicones can be implanted in the human body (for example, in breast implants or catheters) without producing immunological rejection. That property of being harmless and compatible with biological systems is called biocompatibility. Therefore statement (b) “They are biocompatible” is also true.

We now examine their thermal and electrical behaviour. The $$\text{Si-O}$$ bond has a very high bond enthalpy (about $$\;452\;\text{kJ mol}^{-1}$$), and the bond angle $$\bigl(\approx 143^\circ\bigr)$$ is large, which hampers rotation-generated strain. These factors make the chain extremely stable toward heat; many silicone oils remain liquid even beyond $$200^{\circ}\text{C}$$. As for electrical properties, silicone oils are frequently used as cable insulators mainly because they do not conduct current. However, when we compare their dielectric strength (the maximum field they can withstand without breakdown) with that of specialised high-voltage transformer oils or cross-linked polyethylene, the value for silicones is somewhat lower. In other words, silicones have high thermal stability but a lower dielectric strength relative to the best insulating fluids. Hence statement (c) “In general, they have high thermal stability and low dielectric strength” is accepted as true.

Finally, we consider their behaviour toward oxidation. The same inertness that makes silicones biocompatible also renders them resistant to atmospheric oxygen. Because they maintain lubricity over a wide temperature range, they are widely used as high-temperature lubricating greases and release agents. Thus statement (d) “Usually, they are resistant to oxidation and used as greases” is likewise true.

All four statements (a), (b), (c) and (d) are therefore correct, so we choose the option that lists every one of them.

Hence, the correct answer is Option C.