Final answer:
The economic concept represented in this situation is altruism. Diya's donation to the World Wildlife Fund without expecting anything in return demonstrates selfless concern for the well-being of others.
Step-by-step explanation:
The economic concept represented in this situation is altruism. Altruism refers to the selfless concern for the well-being of others. In this case, Diya is choosing to donate $5 to the World Wildlife Fund without expecting anything in return, which aligns with the concept of altruism. Her name being written on a heart decal in the store's window is a simple acknowledgment of her donation.