(i) Monopoly has been derived from two words 'Mono' - single, 'poly' - to control.
(ii) Monopoly is a market situation in which there is only one seller.
(iii) There is no scope for competition.

(i) Very short period (or) Market Period
(ii) Short period
(iii) Long-period
(iv) Very long period (or) Secular period

Excess capacity is the difference between the optimum output that can be produced and the actual output produced by the firm.

A person who has no power to fix the price of the product is a price taker. A seller in perfect competition is a price taker.

Market refers to a system of exchange between the buyers and the sellers of a commodity.

(i) Large number of buyers and sellers.
(ii) They are price makers. They set their own prices.
(iii) Firms produce differentiate products.
(iv) Free entry and exit.
(v) It follows an independent price policy.
(vi) Non-price competition is essential.
(vii) Expenditure on sale promotion of their products.

(i) It is a market structure in which there is only one buyer of a good or service.
(ii) If there is only one customer for a certain good that customer has 'Monopsony' power in the market for that good.
(iii) Monopsony is analogous to monopoly. But monopoly has market power on the demand side rather than the supply side.

There are three types of price discrimination. They are,
(i) Personal
(ii) Geographical
(iii) On the basis of use
Personal:
(i) Different prices are charged for different individuals.
(ii) For Example: Railway Ticket
Geographical:
(i) Different prices are charged at different places for the same product.
(ii) For Example: A book sold within India at a price is sold in a foreign country at a different price.
On the basis of use:
(i) Different prices are charged for the same product on the basis of use.
(ii) For Example: Electricity board in .domestic and commercial.

(i) In duopoly there are only two sellers.
(ii) Each seller is fully aware of his rival's motive and actions.
(iii) Both sellers may collude.
(iv) They may enter into cut-throat competition.
(v) There is no product differentiation.
(vi) They fix the price to get maximum profit.

Firm : A single production unit in an industry, producing a large or a small amount of the commodity. (eg) Hamam, Lux are 2 firms.
Industry : A group of firms producing the same product. (eg) soap industry.

Long run equilibrium of the firm and group equilibrium:
(i) In the short run under monopolistic competition, the firm earns supernormal profit or loss.
(ii) But in the long run, the entry of new firms will wipe out supernormal profit.
(iii) And the loss experienced by existing firms, monopolists leaving the industry.
(iv) Hence, the firm will earn the only normal profit in the long run.
(v) In the long run, AR curve is more elastic or flatter due to plenty of substitutes available.

(vi) At Point E the firm achieves the equilibrium where MC = MR.
(vii) OP - Price, OM - Output
(viii) MQ - Average Cost, M = Average Revenue
\(\therefore\) MQ = MQ (AR = AC)
(ix) It means a firm earn the only normal profit in the long run.

Here the market is classified not only on its geographical spread but also nature of goods.

(i) Local Market:
1. The products exchanged are mostly perishable and semi-durable in nature.
2. For Example Halva in Tirunelveli.
(ii) Provincial Market:
1. Products are sold and bought in a restricted circle
2. For Example Provincial newspaper
(iii) National Market:
1. Products are sold and bought throughout a country is called national market.
2. For Example Tea, Coffee etc.
(iv) International Market:
1. Products are sold and bought at the world level are called international market.
2. For Example Petrol, Gold, etc.

(i) A monopoly is a one firm industry.
(ii) It has a downward sloping demand or AR curve.
(iii) More units of output are sold at less price.
(iv) MR lies below AR.
(v) The monopolist will continue to sell his product as MR > MC. Equilibrium is when MC = MR.
(vi) Beyond this point the producer has loss.

At OM output MC = MR. Beyond OM he will stop production since MC > MR.
At equilibrium average revenue = QM
Average cost = RM
Profit per unit = RQ
Total profit = PQRS