Rusting is an electrochemical process. Justify. If two iron articles are coated with tin and zinc respectively, in which case will the rusting of iron be more rapid, if the coating is worn out in one place. Give a reason.

Explanation

Iron when exposed to humid atmosphere gets converted to `Fe^(2+)` due to the formation of `Fe (OH)_(2)` and this is in presence of air `(O_(2))` to form rust. `Fe_(2)O_(3). XH_(2)O`
When tin coating on iron is broken iron gets exposed to atmosphere. Since iron has greater oxidation potential than tin, iron acts as anode and tin acts as cathode. Iron gets oxidised to `Fe^(+2)` ions in preference to tin. Consequently rusting becomes rapid when tin coating on iron is broken. Since Zn has greater oxidation potential than Fe, though Zinc is worn out, Zn present on the rest of the article gets oxidised in preference to Fe. Hence, rusting of Fe is slow.