The cross linked polymers will be formed by $$RSiC{l_3}$$

The correct choice is (c)

Polymerisation starts either by condensation or addition reactions between monomers. Condensation polymers are formed by the combination of monomers with the elimination of simple molecules. Where as the addition polymers are formed by the addition together of the molecules of the monomer or monomers to form a large molecule without elimination of any thing.

The monomer units of nylon-66 are obtained by the reaction of hexamethylene diamine and adipic acid.
Nylon-66 contain polyamide bond and show condensation.

Phenol is condensed with formaldehyde in presence of either, an acid or a base. In first step $$o{\text{ - }}$$  and /or $$p$$ - hydroxymethyl phenol is formed which further reacts with phenol to give Novolac. On further heating with formaldehyde, novolac undergoes cross linking to an infusible solid known as bakelite.

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Polymers which change irreversibly into hard and rigid material on heating are known as thermosetting polymers e.g bakelite.

$$S{F_6}$$  is used in the vulcanisation of rubber. Sulphur is heated with polymer to introduce cross-linking and thus, form tough polymer.

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In polymerisation of 1, 3 - butadiene either 1, 4 - polymerisation or 1, 2 - polymerisation occurs. In case of 1, 4 - polymerisation, the double bond shifts at \[{{C}_{2}}\]  and \[{{C}_{4}}\]  carbon, while the chain propagates from \[{{C}_{1}}\] and \[{{C}_{4}}\]  end. In this either trans or $$cis$$  polymeric chain is formed.
Option (A) and (B) represent $$'trans'$$  and $$'cis'$$  1, 4 polymerisation respectively. Option (C) resembles 1, 2 polymerisation, where as option (D) most unlikely to happen.