O2 is the oxidizing agent as it gains electrons and is reduced to H2O.

Zinc (Zn) is oxidized to Zn2+, so its oxidation state is +2.

Iron (Fe) is oxidized as it loses electrons to form FeCl3.

Fe2O3 is reduced to Fe, as it gains electrons during the reaction.

Magnesium is oxidized as it loses electrons and its oxidation state increases from 0 to +2.

N2 is reduced to NH3 as it gains electrons.

Iron (Fe) is oxidized as it loses electrons to form Fe2O3.

Copper (Cu) is reduced as it gains electrons from zinc.

Cu is oxidized to Cu2+ as it loses electrons in the reaction.

Zn is oxidized to Zn2+ as it loses electrons.

In C2O4^2-, the oxidation state of carbon is +3.

In NaClO3, the oxidation state of chlorine is +5. Sodium is +1 and each oxygen is -2, leading to the equation: +1 + x + 3(-2) = 0, solving gives x = +5.

In NH4+, nitrogen has an oxidation state of -3. Each hydrogen is +1, leading to the equation: x + 4(+1) = +1, solving gives x = -3.

In H2SO4, the oxidation state of sulfur is +6. Each hydrogen is +1 and each oxygen is -2, leading to the equation: 2(+1) + x + 4(-2) = 0, solving gives x = +6.

In acidic medium, Cr2O7^2- is reduced to Cr^3+.

C2O4^2- (oxalate ion) is oxidized to CO2, thus it acts as a reducing agent in this reaction.

H2O → H2 + O2 involves the oxidation of water to hydrogen and oxygen, making it a redox reaction.

Carbon (C) acts as a reducing agent as it donates electrons to reduce Fe2O3 to Fe.

Reduction is defined as the gain of electrons, and it always occurs simultaneously with oxidation in redox reactions.