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

1. Orthosilicates: ${\text{SiO}}_4^{4-}$ (discrete tetrahedra).2. Pyrosilicates: ${\text{Si}}_2{\text{O}}_7^{6-}$ (two tetrahedra sharing one oxygen).3. Chain silicates (pyroxenes): $({\text{SiO}}_3^{2-}{)}_n$ (sharing two oxygen atoms per tetrahedron).4. Sheet silicates: $({\text{Si}}_2{\text{O}}_5^{2-}{)}_n$ (sharing three oxygen atoms).