Amaira is a seven year old girl. She planned with her father to give a gift on her mother's birthday. She took her piggy bank to shopkeeper with her father. She selected a purse for her mother and when she took out one not of Rs 1000 from the piggy bank the shopkeeper refused to take that not -saying that it is no longer a valid currency . her father explained her that shopkeeper is saying right.
(i) Identify the concept discussed in above para.
(ii) State three feature of that concept.