(i) Expenditure involved in selling the product is called selling cost.
(ii) It is the cost incurred to alter the position of the demand curve for a product. (eg) advertisement.
(iii) Sales promotion by advertisement is called non-price competition.

First degree price discrimination:
(i) A monopolist charges the maximum price that a buyer is willing to pay.
(ii) This is perfect price discrimination.
(iii) Consumer's surplus is zero.
Second degree price discrimination:
(i) Price charged is such that a part of consumer's surplus is taken away by the sellers.
(ii) This is called imperfect discriminating monopoly.
(iii) Buyers are divided into groups and a different price is charged for each group. (eg) cinema theaters charge different price for the same film for different class.
Third degree price discrimination
(i) The entire market is split into a few sub markets and different prices are charged in each sub market.
(ii) The division is done based on age, sex, location. (eg) senior citizens pay lower fares in railways.

In perfect competition there is freedom for new firms to enter into the industry but in monopoly no competitor can enter the market except for the monopolist.

(i) Buyers and sellers of a commodity or a service. A commodity is bought and sold.
(ii) Price agreeable to buyer and seller.
(iii) Direct exchange and indirect exchange.