A solution of an electrolyte can be stored in a particular vessel only in case there is no chemical reaction taking place with the material of the vessel.
Now if silver nitrate solution is to be kept in copper vessel, the probabel reaction will be :
`Cu(s)+2Ag^(+)(aq) to Cu^(+)+2Ag(s)`
Since copper is placed below silver in the activity series, this means that it is a stronger reducing agent and can lose electrons to `Ag^(+)` ions and the chemical reaction will occur. Therefore, silver nitrate is a stronger reducing agent and solution cannot be kept in copper vessel. Now, when copper sulphate solution is placed in silver vessel, the likely chemical reaction is :
`2Ag(s)+Cu^(2+)(aq) to Cu(s)+2Ag^(+)(aq)`
Since Ag is placed above copper in the activity series, the chemical reaction will not take place. As a result, copper sulphate can be easily stored in silver vessel.