1. Regulation is most likely to occur in a market characterized as

a. monopolistically competitive.

b. perfectly competitive.

c. oligopolistic.

2. Regulation is most likely to occur in a market with a Herfindahl–Hirschman Index (HHI) of

a. 100

b. 1000

c. 5

d. 2500

3. Regulation is more likely to occur in

a. broadly defined markets.

b. narrowly defined markets.

c. oligopolistic. 

d. 2500 

a. broadly defined markets. 

Explanation:

An oligopoly is when there are few large firms in an industry. There are high barriers to entry of firms into the industry. The firms set the market price. Because, the firms may sometimes engage in activities such as setting high prices to maximise profits which is disadvantageous to consumers, government sometimes have to intervene in their activities.

A perfect competition is characterised by many buyers and sellers of homogenous goods and services. Firms ams consumers are price takers. There are no barriers to entry of exit of firms

A monopolistically competitive firm is characterised by many buyers and sellers of differentiated goods.

The HHI index is used to determine the concentration ratio of firms in an industry.

An industry with HHI of less than 1,500 is considered to be a competitive, an HHI of 1,500 to 2,500 to be a moderately concentrated, and an HHI of 2,500 or greater to be a highly concentrated industries . Regulation usually occurs in highly concentrated industries.

In broadly defined markets, it is more difficult to find close subsituites for goods and services so demand is usually inelastic. Because demand is relatively inelastic, firms might have the incentive to increase prices of their goods to maximise profits. This is why regulation might be necessary.

I hope my answer helps you