Which of the following reaction involves neither oxidation nor reduction

• A. \[CrO_{4}^{2-}\to C{{r}_{2}}O_{7}^{2-}\]
• B. \[Cr\to CrC{{l}_{3}}\]
• C. \[Na\to N{{a}^{+}}\]
• D. \[2{{S}_{2}}O_{3}^{2-}\to {{S}_{4}}O_{6}^{2-}\]