Answer: B) hydroxide
Explanation: Redox reactions have oxidation and reduction half equations. The could take place in acidic or basic medium.
First of all we write the oxidation and reduction half equations then balance all the atoms other than oxygen and hydrogen. Then oxygen is balanced by adding [tex]H_2O[/tex] and hydrogen is balanced by adding [tex]H^+[/tex] . Finally the charge is balanced by adding electrons and then we make the electrons equal for both the half equations for which the equations ma need to be multiplied by integers.
Then the half equations and are added and common species like electrons are canceled.
Now the important point, If the reaction is taking place in acidic medium then what we have done is all but if the reaction is taking place in basic medium then we add [tex]OH^-[/tex] to both sides and its equal to the number of [tex]H^+[/tex] present in the equation that we got so far.
Hydrogen ion and hydroxide ion combine to form water.
So, in basic medium, hydroxide is added to balance half reactions.
