Question

Which two metals do not corrode easily $ ? $ give examples in each case to support that corrosion in some metals are advantageous .

Answer 1

Hint : Metals get corroded when they react with hydrogen , oxygen and form hydrides , oxides ,sulphides . It is destruction of the metals by the chemical reactions occurring due to the environment . The formation of rust on iron, tarnish on silver and blue green patina that develops on copper are all due to corrosion .

Complete step by step answer:
Gold and platinum are metals that do not corrode easily . They both have high resistivity towards corrosion . They are also unaffected by acids ,oxygen . so they are termed as noble metals .
In some metals corrosion is referred as advantage because :
A layer is formed due to corrosion which helps the inner metal layer to stay safe .
Like in aluminium , on which a layer of aluminium oxide is formed which then protects the aluminium from further destruction .
 It is also useful in cathodic protection , in which the underground pipes are protected . In this the pipes are connected with more active metal which gets corrode easily like zinc . so, here the zinc acts as a sacrificial anode and the pipe acts as a cathode which is being protected . One advantage of this method is that the sacrificial anode can be monitored and easily replaced whenever needed.

Additional Information
The chemical of rust is $ F{e_2}{O_3}.x{H_2}O $ which is a hydrated iron oxide . Here the number of water molecules is variable and represented as x. Large amount of money is spent every year due to corrosion . But corrosion can be prevented by coating the metals with paints . The paints will slow down this process .

Note:
The statue of liberty was in brown colour but it appeared blue green colour today ,this is due to corrosion . The primary component of the Statue of liberty underwent oxidation from the air and thus changed in the colour of it .