i. "3H"_2"O" + "BH"_4^"-" -> "H"_2"BO"_3^"-" + "8H"^"+" + 6"e"^"-"
ii. "6H"^"+" + "ClO"_3^"-" + 6"e"^"-" -> "Cl"^"-" + "3H"_2"O"
iii.
1×[color(red)(cancel(color(black)("3H"_2"O"))) + "BH"_4^"-" -> "H"_2"BO"_3^"-" + stackrelcolor(blue)(2)(color(red)(cancel(color(black)(8))))"H"^"+" + color(red)(cancel(color(black)(6"e"^"-")))]
1×ul([color(red)(cancel(color(black)("6H"^"+"))) + "ClO"_3^"-" + color(red)(cancel(color(black)(6"e"^"-"))) -> "Cl"^"-" + color(red)(cancel(color(black)("3H"_2"O")))])
color(white)(mmm)"BH"_4^"-" + "ClO"_3^"-" -> "H"_2"BO"_3^"-" + "2H"^"+" + "Cl"^"-"
iv.
1×["MnO"_4^"-" + 8"H"^"+" + color(red)(cancel(color(black)(5"e"^"-")))→ "Mn"^"2+" + 4"H"_2"O"]
5×ul(["Fe"^"2+" → "Fe"^"3+" + color(red)(cancel(color(black)("e"^"-")))]color(white)(mmmmmmmmmmmmmml))
color(white)(mml)"MnO"_4^"-" + "5Fe"^"2+" + "8H"^"+"→ "Mn"^"2+" + "5Fe"^"3+" + 4"H"_2"O"
