The Zn acts as sacrificial or cathodic protection to prevent rusting of iron because:

1. $E_{OP}^{\circ }$ of Zn < $E_{OP}^{\circ }$ of Fe

2. $E_{OP}^{\circ }$ of Zn > $E_{OP}^{\circ }$ of Fe

3. $E_{OP}^{\circ }$ of Zn = $E_{OP}^{\circ }$ of fe

4. Zn is cheaper than iron

The cell reaction of micro electrochemical cell formed during rusting of iron is:-

1.  ${\mathrm{O}}_2\left(\mathrm{g}\right) + 4{\mathrm{H}}^{\oplus }\left(\mathrm{aq}\right) + 4{\mathrm{e}}^{-} \to 2{\mathrm{H}}_2\mathrm{O} \left(\mathrm{l}\right)$

2. $4{\mathrm{Fe}}^{+2}\left(\mathrm{aq}\right) + {\mathrm{O}}_2\left(\mathrm{g}\right) + 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \to 4\mathrm{FeO} + 4{\mathrm{H}}^{\oplus }\left(\mathrm{aq}\right)$

3. $2\mathrm{Fe}\left(\mathrm{s}\right) + {\mathrm{O}}_2\left(\mathrm{g}\right) + 4\mathrm{H}{°}^{\oplus }\left(\mathrm{aq}\right) \to 2{\mathrm{Fe}}^{+2}\left(\mathrm{aq}\right) + 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)$

4.  $\mathrm{Fe}\left(\mathrm{s}\right) \to {\mathrm{Fe}}^{+2}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-}$