$(a)$ Why is the corrosion of iron a serious problem?
$(b)$ How can we prevent corrosion?

(N/A) Corrosion of iron is a serious problem because it causes significant structural damage to bridges,iron railings,ships,and all objects made of metals,especially those made of iron. Every year,an enormous amount of money is spent to replace damaged iron structures.
$(b)$ Corrosion can be prevented by several methods:
$1$. Painting: Applying a coat of paint on the surface of the iron object.
$2$. Galvanization: Coating iron with a thin layer of zinc.
$3$. Electroplating: Depositing a layer of a non-corrosive metal over the iron surface.
$4$. Greasing or Oiling: Applying oil or grease to moving parts of machines.