Balance the following ionic equations:
$1. Cr_{2}O_{7}^{2-} + H^{+} + I^{-} \to Cr^{3+} + I_{2} + H_{2}O$
$2. Cr_{2}O_{7}^{2-} + Fe^{2+} + H^{+} \to Cr^{3+} + Fe^{3+} + H_{2}O$
$3. MnO_{4}^{-} + SO_{3}^{2-} + H^{+} \to Mn^{2+} + SO_{4}^{2-} + H_{2}O$
$4. MnO_{4}^{-} + H^{+} + Br^{-} \to Mn^{2+} + Br_{2} + H_{2}O$

(A) To balance the redox reactions,we use the ion-electron method:
$1. Cr_{2}O_{7}^{2-} + 14H^{+} + 6I^{-} \to 2Cr^{3+} + 3I_{2} + 7H_{2}O$
$2. Cr_{2}O_{7}^{2-} + 6Fe^{2+} + 14H^{+} \to 2Cr^{3+} + 6Fe^{3+} + 7H_{2}O$
$3. 2MnO_{4}^{-} + 5SO_{3}^{2-} + 6H^{+} \to 2Mn^{2+} + 5SO_{4}^{2-} + 3H_{2}O$
$4. 2MnO_{4}^{-} + 16H^{+} + 10Br^{-} \to 2Mn^{2+} + 5Br_{2} + 8H_{2}O$