Answer:
Metallic iron will rust (oxidize) into iron (II) oxide in presence of oxygen, and water.
Corrosion (rust) is a redox reaction. This kind of reaction involves the oxidation of Iron. In any redox reaction there is a transfer of electrons. The presence of salt in water increases the rate of reaction because it increases the conductivity of water. If we increase the concentration of ions in water the electrons will be transferred more easily and the corrosion will be accelerated.
In conclusion, the presence of salt in the water accelerates the rustin process but is not the cause.