The reaction in which the more reactive metal displaces the less reactive metal from its compound or most accurately t's salt is known as displacement reaction.
The above question is an example of displacement reaction.
As we know about the reactivity series which explains that the Al metal is more reactive than the copper metal.So here when the copper sulphate is poured into the aluminium can the aluminium(more reactive metal) replaces copper(less reactive than copper) from the copper sulphate solution.Now since the aluminium layers of the can gets engaged with the sulphate to form aluminium sulphate.Therefore,the places from where these aluminium particles react with copper sulphate,some sort of holes appears indicating that the reaction has taken place.
The above reaction can be represented as follows:-
4Al (s) +2CuSO4 -----> 2Al2(SO4)3 +2Cu
but why
literally asked. not to worry.
ok fine
A metal displaces other from salt solution if the metal is more reactive than metal of salt solution.
now aluminium is more reactive than cu that's why aluminium reacts with solution and there are holes in can.this can be the reason. but there's also a fact that aluminium reacts with atmospheric substances and produces layer of aluminium oxide on its surface which prevents it from reacting with other substances.