Q.The repeating unit in silicone is

Silicones (polysiloxanes) are organosilicon polymers of general formula (R₂SiO) -- so named because the formula formally resembles a ketone's R₂CO. They are generally made by hydrolysing dialkyl/diaryldichlorosilanes (R₂SiCl₂/Ar₂SiCl₂), themselves made by passing RCl/ArCl vapour over heated silicon with a copper catalyst; hydrolysis-and-condensation of R₂SiCl₂ builds a self-extending linear -[SiR₂-O]- chain, while hydrolysing the more heavily chlorinated RSiCl₃ gives a cross-linked polymer instead, since each silicon then has three chlorines available to become Si-O-Si links.

Three structural types: (i) linear silicones (from R₂SiCl₂), further split into silicone rubbers (bridged by methylene-type groups) and silicone resins (blended with organic resins); (ii) cyclic silicones, made by closing a linear chain's two terminal -OH groups into a ring; (iii) cross-linked silicones, from RSiCl₃. …