Which are the various forms of silica?

For correct statement use $T$ and for incorrect use $F$:
$(A)$ Hydrolysis of Marshall's acid gives $H_2SO_4$ and $H_2O_2$ as final products.
$(B)$ In $SCNSiH_3$ structure,the geometry around $N$ is bent.
$(C)$ The basic unit for silicates is $SiO_4^{4-}$.
$(D)$ $NH_4Cl + NaOH \to NH_3 \uparrow$.

On hydrolysis,$(Me)_2SiCl_2$ will produce:

The common basic structural unit in silicates and silica is

Which one of the following is a correct set?

Element showing the phenomenon of allotropy is