Which of the following type of compound is used to increase the hardness of the silicone polymer.

Hardness of silicone polymer increases if polymer has the maximum number of R₂SiO units attach to it. If silicone polymer opt a 3D structure, the it enhances the hardness of silicone.

The hydrolysis of RSiCl₃ gives RSi(OH)₃.

${\mathrm{RSiCl}}_3+3{\mathrm{H}}_2\mathrm{O}\to \mathrm{RSi}{\left(\mathrm{OH}\right)}_3+3\mathrm{HCl}$

There are three -OH groups in RSi(OH)₃, hence it can undergo condensation from three sides using three -OH groups and form polymer that has 3D structure. This enhances the hardness of the polymer.