The correct option is
A SiO4−4The basic unit of silicates is
SiO4−4 as each silicon atom is bonded with 4 oxide ions tetrahedrally.
The different types of silicates are:
1) Orthosilicates- Contains one unit of SiO4−4 eg [Zn2SiO4]
2) Pyrosilicates - Contains two unit of SiO4−4 along an oxygen atom eg-Si2O6−7
3) Cyclic or ring: The general formula is SiO2−3 eg-Si3O6−9 Beryl - Be3Al2Si6O18
4) Chain silicates- These are formed by sharing 20 oxygen atoms by each tetrahedral. The general formula is :
a)(SiO3)2n−n
b)(Si4O11)6n−n
5) Two-dimensional sheet silicates: In this 3 oxygen atoms of each tetrahedral are shared with two adjacent SO4−4 tetrahedral. The general formula is (Si2O5)2n−n
6) Three-dimensional sheet silicates: In these all four oxygen atoms are shared with adjacent SiO4−4 tetrahedral.