Arranged by decreasing bond length:
1. \(\mathrm{SiO}_4^{4-}\) : Silicon has the largest atomic radius and the lowest oxidation state, leading to the longest bond lengths.
2. \(\mathrm{PO}_4^{3-}\) : Phosphorus is smaller than silicon but has a higher oxidation state.
3. \(\mathrm{SO}_4^{2-}\) : Sulfur is smaller than phosphorus and has a higher oxidation state.
4. \(\mathrm{ClO}_4^{-}\): Chlorine has the smallest atomic radius and the highest oxidation state, resulting in the shortest bond lengths.
Thus, the correct order of decreasing \(\mathrm{X}-\mathrm{O}\) bond length is:
(2) \(\mathrm{SiO}_4^{4-}, \mathrm{PO}_4^{3-}, \mathrm{SO}_4^{2-}, \mathrm{ClO}_4^{-}\)
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