Which of the following is heated with silica at high temperature to obtain carborundum?

Which one of the following is present in the chain structure of silicates?

The number of non-ionisable protons present in the product $B$ obtained from the following reaction is:
$3C_{2}H_{5}OH + PCl_{3} \rightarrow 3C_{2}H_{5}Cl + H_{3}PO_{3} (A)$
$H_{3}PO_{3} + PCl_{3} \rightarrow H_{4}P_{2}O_{5} (B) + HCl$

Match the following:

List-$I$ (Compound)	List-$II$ (Silicate)
$A$. Zircon $(ZrSiO_4)$	$P$. Ring/Cyclic
$B$. Talc $(Mg_3(OH)_2(Si_2O_5)_2)$	$Q$. Ortho
$C$. Thortveitite $(Sc_2Si_2O_7)$	$R$. Pyro
$D$. Benitoite $(BaTiSi_3O_9)$	$S$. Sheet

Amphibole silicate structure has '$x$' number of corners shared per tetrahedron. The value of '$x$' is

What are silicones?