Cho sơ đồ chuyển hóa sau:
\(\begin{gathered} Cr\xrightarrow{{(1)}}CrC{l_2}\xrightarrow{{(3)}}Cr{(OH)_2}\xrightarrow{{(5)}}Cr{(OH)_3}\xrightarrow{{(7)}}NaCr{O_2} \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(2) \downarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(4) \downarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(6) \downarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(8) \downarrow \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,CrC{l_3}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{r_2}{O_3}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,CrC{l_3}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,N{a_2}Cr{O_4} \hfill \\ \end{gathered} \)
Số phản ứng oxi hóa-khử xảy ra trong sơ đồ trên là:
A.6
B.7
C.5
D.4
