$\text{Cl}_2 + 2\text{H}_2\text{O} + \text{SO}_2 \longrightarrow 4\text{H}^+ + \text{SO}_4^{2-} + 2\text{Cl}^-$

$\text{Cu}^{2+} + \text{Zn} \longrightarrow \text{Cu} + \text{Zn}^{2+}$

$2\text{H}_2 + \text{O}_2 \longrightarrow 2\text{H}_2\text{O}$

$\text{HCl} + \text{H}_2\text{O} \longrightarrow \text{H}_3\text{O}^+ + \text{Cl}^-$

$+2$

$+4$

$+3$

$+7$

Removal of oxygen

Addition of electronegative element

Addition of electropositive element

Gain of electron

$-2$

$-1/2$

$-1$

$+2$