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.  ${\mathrm{O}}_2\left(\mathrm{g}\right)<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>4{\mathrm{H}}^{\oplus }\left(\mathrm{aq}\right)<mspace\; width="1em"></mspace><mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>4{\mathrm{e}}^{-}<mspace\; width="1em"></mspace>\to <mspace\; width="1em"></mspace>2{\mathrm{H}}_2\mathrm{O}<mspace\; width="1em"></mspace>\left(\mathrm{l}\right)$

2. $4{\mathrm{Fe}}^{+2}\left(\mathrm{aq}\right)<mspace\; width="1em"></mspace><mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>{\mathrm{O}}_2\left(\mathrm{g}\right)<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)<mspace\; width="1em"></mspace>\to <mspace\; width="1em"></mspace>4\mathrm{FeO}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>4{\mathrm{H}}^{\oplus }\left(\mathrm{aq}\right)$

3. $2\mathrm{Fe}\left(\mathrm{s}\right)<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>{\mathrm{O}}_2\left(\mathrm{g}\right)<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>4\mathrm{H}{°}^{\oplus }\left(\mathrm{aq}\right)<mspace\; width="1em"></mspace>\to 2{\mathrm{Fe}}^{+2}\left(\mathrm{aq}\right)<mspace\; width="1em"></mspace><mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)$

4.  $\mathrm{Fe}\left(\mathrm{s}\right)<mspace\; width="1em"></mspace>\to {\mathrm{Fe}}^{+2}\left(\mathrm{aq}\right)<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>2{\mathrm{e}}^{-}$