$X_2Cl_3\Rightarrow X^{3+}Cl^{2-}$

$X_2(SO_4)_3\Rightarrow X^{3+}SO_4^{2-}$

$XPO_4\Rightarrow X^{3+}PO_4^{3-}$

Because $Cl^{2-}$ does not exist. So, $X_2Cl_3$ is incorrect. The correct formula should be $XCl_3$.