Explanation

(b)
The structure of silicates has been found with the help of X-ray diffraction technique. All silicates have tetrahedral $SiO_{4}^{4 -}$ ion as a basic building unit $i.e.,$ all silicates are composed of many units. Tetrahedral shape of $\left\lbrack SiO_{4} \right\rbrack^{4 -}$ ion is due to $sp^{3}$-hybridisation of Si-atom. Sheet silicates are formed when three oxygen atoms (bridging O-atoms) of each $\left( SiO_{4} \right)^{4 -}$ unit are shared. Hence, the general formula of sheet silicates is $\left( Si_{2}O_{5} \right)^{2n -}$
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