Answer:2) rule of reciprocity
Explanation:
The rule of reciprocity is our social norm to return the favour when someone else has done something for us , there is always a human need or felt obligation to do something back.
Marketing is one field that uses this rule mostly in which marketers come up with various strategies that can bring customers to buying their product such as you buy two get one free.
Marketers use promotions, sales and coupons to attract customers.
