The correct option is A Both A and R are true and R is the correct explanation of A.
An electroscope can be used to find the presence of charge on a body.
When a charged object is touched by the metal disk, the charges are transferred to the metal strips of the electroscope. Both the strips gain similar charges and start repelling each other. This is because like charges repel.
Uncharged bodies do not change the position of the metal strip.
Therefore, both A and R are true and R is the correct explanation of A.