An electroscope is used to detect whether a body is charged or not.
It consists of a metal rod in which one end of the rod is fixed with two leaves of aluminium foil, while the other end has a metal disc. The leaves of aluminium foil are placed inside a beaker and the beaker is covered with a insulating rubber cork to prevent the entry of air into the beaker.
When the metal disc is touched with a charged body either positively charged body or negatively charged body, it is observed that the aluminium strips move away from each other.
This happens because the metallic disc conducts/transfers the charges towards the aluminium leaves, and as same charges get accumulated in the two aluminium leaves, thus they repel each other and move away from each other. This shows that conduction is taking place in the electroscope from the metallic disc to the aluminium leaves through the metallic rod.
Even if the charged body is removed from touching the metallic disc, then also the aluminium leaves are seen to be present, away from each other as the same charges are still present in them.