← Unit 1: Markets in Action

Market Failure Model Answers

Section 1.3.5 — Annotated model answers for negative externalities, public goods, merit goods, and market failure questions.

These model answers demonstrate how to structure responses for Edexcel International A-Level (IAL) Economics and Business exams. Each answer includes a mark scheme breakdown, PEEL structure (where applicable), annotated paragraphs, and examiner commentary explaining what earns marks at each band.
Filter by marks:
4 marks
Unit 1 · 1.3.5 Market Failure · Knowledge & Application
Explain: what is meant by a negative externality and give one example.
Mark Scheme Breakdown
1–2 marksDefinition of negative externality (spill-over cost to third parties not reflected in price)
3–4 marksClear, developed example with reference to third-party cost and market over-production
KKnowledge/Definition
EExample
AApplication
Model Answer
A negative externality is a spill-over cost imposed on third parties K who are not involved in the transaction between producer and consumer, and is therefore not reflected in the market price. K

For example, a coal-fired power station E emits carbon dioxide and sulphur dioxide as by-products of electricity production. Local residents and future generations suffer increased rates of respiratory illness and climate-related damage — costs they bear without compensation. A Because these social costs are external to the firm's calculations, the market over-produces electricity relative to the socially optimal output. A
Examiner Commentary

Full marks require both a precise definition (spill-over cost, third parties, not in price) and a developed example that identifies the specific third-party harm. Vague answers like "pollution affects people" will only reach 2 marks. Linking over-production to the divergence between private and social cost pushes into top-band application.

Likely Score4 / 4
8 marks
Unit 1 · 1.3.5 Market Failure · Analysis
Analyse: how a negative externality of production leads to market failure.
Mark Scheme Breakdown
1–2 marksKnowledge: definition of negative externality, social cost > private cost
3–4 marksApplication: named example (e.g. factory pollution)
5–8 marksAnalysis: welfare loss diagram, overproduction, price too low, third-party harm
PEEL Structure
P
Point

A negative externality causes the market to overproduce because the price does not reflect the full social cost.

E
Evidence

E.g. a steel factory discharging pollutants into a river — harming fisheries downstream.

E
Explain

The producer only considers private costs (raw materials, wages). The external cost (pollution damage) is not included in the price, so the market price is too low and output too high relative to the social optimum.

L
Link

This misallocation of resources creates a deadweight welfare loss — society would be better off producing less.

KKnowledge
AApplication
AnAnalysis chain
DDiagram ref.
Model Answer
Para 1
A negative externality of production occurs when the production of a good imposes costs on third parties who are not involved in the transaction. K In this case, the marginal social cost (MSC) exceeds the marginal private cost (MPC) — the gap between them represents the external cost. K
Para 2
For example, a steel factory discharging chemical waste into a nearby river imposes costs on downstream fisheries, local residents, and the environment. A The factory only considers its private costs (raw materials, energy, wages) when deciding how much to produce. It does not pay for the pollution damage — this external cost falls on third parties. An
Para 3
Because the market price reflects only private costs, not social costs, the price is too low and output is too high relative to the socially optimal level. An On a diagram, the free market produces at Q₁ (where MPC = MPB) but the social optimum is at Q* (where MSC = MSB). The area between Q* and Q₁, bounded by MSC and MSB, represents the deadweight welfare loss — the excess cost to society from overproduction. D An
Para 4
This is a clear case of market failure because the price mechanism sends the wrong signal — it tells producers to produce more than is socially desirable. An Resources are misallocated because the market does not account for the full cost of production. Government intervention (e.g. a Pigouvian tax equal to the external cost) could internalise the externality and move output toward the social optimum. An
Examiner Commentary

Excellent chain of reasoning: external cost → MSC > MPC → price too low → overproduction → welfare loss. The steel factory example provides strong application. The diagram reference is essential for top marks. The mention of a Pigouvian tax shows evaluative awareness without being asked to evaluate.

Likely Score7–8 / 8
20 marks
Unit 1 · 1.3.5 Market Failure · Evaluation Essay
Evaluate: the view that government intervention is always necessary to correct market failure.
Mark Scheme Breakdown
AO1 (4 marks)Knowledge of market failure types and government intervention methods
AO2 (4 marks)Application — relevant examples of market failure and intervention
AO3 (6 marks)Analysis — chains of reasoning for and against intervention
AO4 (6 marks)Evaluation — government failure, Coase theorem, context-dependent judgement
PEEL Structure
P
Point

Government intervention can correct externalities, provide public goods, and address information failure.

E
Evidence

E.g. the UK's sugar tax reduced sugary drink consumption by 34% within two years.

E
Explain

Intervention internalises external costs (taxes), funds provision of public goods (taxation), and corrects information asymmetry (regulation, labelling).

L
Link

However, intervention is not always necessary or effective — private solutions (Coase theorem) may work, and government failure can make outcomes worse.

KKnowledge
AApplication
AnAnalysis chain
Model Answer
Introduction
Market failure occurs when the free market leads to a misallocation of resources — producing too much (negative externalities), too little (positive externalities, merit goods), or none at all (public goods). K The question is whether government intervention is always required to correct these failures, or whether alternative mechanisms — including private bargaining and market-based solutions — can sometimes achieve efficient outcomes without state action. An
Argument 1 — Intervention is necessary
In many cases, government intervention is essential because the market cannot self-correct. An Public goods such as street lighting and national defence are non-excludable and non-rivalrous — the free rider problem means no private firm can profitably supply them. Only the state can fund provision through taxation. K Similarly, negative externalities require intervention because firms have no incentive to account for external costs. The UK's sugar tax (Soft Drinks Industry Levy), introduced in 2018, successfully reduced sugary drink consumption by 34% and incentivised manufacturers to reformulate products. A Without this intervention, the overconsumption of sugar — and its associated NHS costs — would have continued uncorrected. An
Argument 2 — Intervention is not always necessary
However, government intervention is not always required. The Coase theorem suggests that if property rights are well-defined and transaction costs are low, private parties can negotiate an efficient outcome without government involvement. K For example, if a factory pollutes a farmer's land and the farmer has clear legal ownership, they can negotiate compensation or a reduction in pollution — reaching the socially optimal output through bargaining. A In practice, however, transaction costs are often high and property rights unclear, limiting the applicability of this approach. An
Evaluation — Government failure
Even when intervention is attempted, it can lead to government failure — where the intervention makes the allocation of resources worse rather than better. K Governments face information failure — they may not know the exact size of an external cost, leading them to set taxes too high or too low. An Regulatory capture means regulators may serve industry interests rather than the public. An Unintended consequences are common — for example, minimum pricing on alcohol may harm low-income moderate drinkers without significantly reducing problem drinking. A The cost of intervention itself (bureaucracy, enforcement, compliance) may exceed the welfare gain from correcting the failure. An
Conclusion
On balance, government intervention is often necessary but not always effective or desirable. For pure public goods and large-scale externalities where private solutions are impractical, intervention is essential. An However, the form and extent of intervention matters — well-designed market-based instruments (tradable permits, targeted taxes) tend to outperform heavy-handed regulation. The key judgement is whether the costs of government failure are likely to be greater or less than the costs of market failure left uncorrected. Where transaction costs are low and property rights clear, private solutions should be tried first. An
Examiner Commentary

This answer earns top marks through its conditional, nuanced conclusion — not simply "yes" or "no" but "it depends on the type of failure and the quality of intervention." The sugar tax and Coase theorem examples provide strong AO2 application. The government failure section with information failure, regulatory capture, and unintended consequences demonstrates sophisticated AO4 evaluation. The final sentence — comparing costs of government failure with costs of market failure — is exactly the evaluative framework examiners reward.

Likely Score18–20 / 20

More Model Answers

Browse all Edexcel IAL Economics & Business model answers with mark scheme breakdowns and examiner commentary.

View All Model Answers →