Question

Read the following short write-up and answer the questions at the end of it The name 'silica' covers an entire group of minerals, which have the general formula $Si{O}_2$, the most common of which is quartz. Quartz is a framework silicate with $Si{O}_4$tetrahedra arranged in spirals. The spirals can turn in a clockwise or anticlockwise direction- a feature that results in there being two mirror images, optically active, varieties of quartz.

The following pictures represent various silicate anions. Their formulae for silicon and oxygen respectively:

• A. $Si{O}_3^{2-}S{i}_3{O}_7^{2-}$
• B. $Si{O}_4^{4-}S{i}_3{O}_{10}^{8-}$
• C. $Si{O}_4^{2-}S{i}_3{O}_9^{2-}$
• D. $Si{O}_3^{4-}S{i}_3{O}_7^{8-}$

Answer 1

The correct option is B $Si{O}_4^{4-}S{i}_3{O}_{10}^{8-}$

The formulas are represented as $Si{O}_4^{4-}S{i}_3{O}_{10}^{8-}$.
Silicon is at the center of a tetrahedron and 4 oxygen atoms are present at four corners.
Hence, $Si{O}_4^{4-}$ represents the formula of the silicate ion. When three tetrahedra are shown linked together, they share corner oxygen atoms. Hence, the formula of the ion becomes $S{i}_3{O}_{10}^{8-}$.