Răspuns: a.
[tex]\sf K_2^{+1}\underline{Cr_2^{+6}} O_7^{-2}+H^{+1}\underline{\underline{I^{-1}}} +H_2^{+1}S^{+6}O_4^{-2}\rightarrow\underline{Cr_2^{+3}} (S^{+6}O_4^{-2})_3+K_2^{+1}S^{+6}O_4^{-2}+\underline{\underline{I_2^0}}+H_2^{+1}O^{-2}[/tex]
[tex]\sf 2I^{-1}\xrightarrow{-2e^-}I_2^0|3\:\:\:oxidare[/tex]
[tex]\sf Cr^{+6}\xrightarrow{+3e^-}Cr^{+3}|\:\:\:reducere[/tex]
Agent oxidant: K₂Cr₂O₇
Agent reducător: HI
K₂Cr₂O₇ + 6HI + 4H₂SO₄ → K₂SO₄ + Cr₂(SO₄)₃ + 3I₂ + 7H₂O
