Which of the following statements about silicates are correct?

ASilicon in each $SiO X_{4}$ unit is $s p^{3}$ hybridised.
BIn the pyrosilicate anion $Si X_{2} O X_{7} X^{6 -}$ the two tetrahedra share two oxygen atoms.
CIn three-dimensional $SiO X_{2}$ every oxygen is shared by two tetrahedra.
DZeolites are neutral frameworks of pure silica containing no aluminium.

Answer: A, C

Each Si has four sigma bonds, so it is

s p^{3}

. In

Si X_{2} O X_{7} X^{6 -}

two tetrahedra share only one oxygen (total O:

4 + 4 - 1 = 7

). In

SiO X_{2}

all four oxygens are shared, so the formula is

SiO X_{\frac{4}{2}}

. Zeolites are aluminosilicates, with Al replacing some Si. Statements 1 and 3 are correct.