2.34 Describe the conditions under which iron rusts

Water and oxygen cause iron to rust, forming hydrated iron (III) oxide. Okay well water isn't needed, but there's oxygen in water, which causes rusting.
Salty water can make iron rust faster because it is an electrolyte (a liquid containing ions which can conduct electricity). If it can conduct electricity it will allow the electrons to flow more easily, and hence speeding up electron loss (because we know that oxidisation can also be described as the loss of electrons)

Fig 1: Rusting over time