(a)Why does aluminium not corrode right through?
(b)What is meant by ‘anodising’? Why is it done?

(a) Aluminium does not corrode right through because aluminium is more reactive than iron(it lies above iron in reactivity series) and forms a layer of aluminium oxide as soon as it comes in contact with moist air. This layer of aluminium oxide is very tough and prevents the aluminium underneath from corroding.

(b) The process of thickening of aluminium oxide layer on the surface of aluminium objects by electrolysis is called anodizing.

It is done to protect aluminium objects from corrosion.