(a) Why is an iron grill painted frequently?
(b) Explain why, though aluminium is more reactive than iron, yet there is less corrosion of aluminium when both are exposed to air.

(a) In order to prevent rusting of the iron grills, it is painted frequently.

(b) Aluminium is more reactive than iron and forms an oxide layer on its surface when comes to contact with air. This is why there is less corrosion of aluminium when both iron and aluminium are exposed to air.