A positive externality in consumption means the social benefit from consuming the good exceeds the private benefit to the buyer, so people tend to underconsume relative to the social optimum. A per-unit subsidy to consumers lowers the price they effectively pay and raises the quantity demanded, nudging private marginal benefit up toward the social marginal benefit. This internalizes part of the external benefit and moves the market toward the efficient level of consumption. A per-unit tax would raise the price further and reduce quantity, worsening underconsumption. A government ban eliminates the good altogether, removing both private use and the external benefits. A price ceiling can create shortages or misallocate resources and doesn’t directly address the positive externality by boosting social benefits.

Social welfare accounting aims to measure society’s overall well‑being by including all effects that spill over to others, not just those captured in market prices. Externalities are effects of economic activity on third parties that prices do not reflect, so to capture the true impact on welfare they must be added into the social welfare measure as social costs or social benefits. Ignoring them would understate or overstate welfare, and focusing only on government budgets misses broader spillover effects beyond public finances. Externalities do affect societal welfare because they change the total costs and benefits to everyone in society. Therefore, adding the social costs or benefits of externalities into the social welfare measure is the best way to describe their treatment.

The main concept here is how tax structure and transfers influence income inequality. A policy that uses a progressive income tax and imposes high estate and gift taxes targets both current income disparities and the concentration of wealth across generations. Progressive taxation taxes higher incomes at higher rates, which reduces after-tax income gaps and funds public transfers and services that support lower- and middle-income households. Estate and gift taxes help limit the lasting accumulation of wealth in the hands of a few, curbing intergenerational transmission of large fortunes that can lock in inequality over time. In contrast, a flat tax with no transfers would be less redistributive, leaving after-tax incomes more unequal. A regressive tax system places a larger burden on lower-income households, widening inequality. Eliminating inheritance taxes removes a mechanism that reduces wealth concentration across generations, allowing inherited wealth to persist and potentially grow.

Information disclosure policies reduce market failure from asymmetric information by making relevant facts about products, services, and risks visible to everyone. When buyers can’t tell quality, markets can be flooded with low-quality goods (the lemons problem). Clear labeling and transparent information let buyers distinguish higher-quality options, leading to better pricing, more informed choices, and trades that reflect true differences in quality. They also help with moral hazard, because when terms, risks, and expected behaviors are disclosed and monitored, parties face clearer incentives and less opportunity to shirk or take excessive risks after a contract is signed. That combination—improved ability to assess quality and aligned incentives—reduces both adverse selection and moral hazard. Withholding information worsens information problems, while relying on prices alone cannot fully fix hidden attributes or incentives.

First-best policy means fully internalizing the externality so the outcome is efficient, with the social marginal benefit exactly equal to the social marginal cost. In this ideal situation there are no administrative costs or distortions, so the policy nudges the market to the efficient quantity—often through a tax per unit equal to the external marginal cost or a corresponding quantity restriction. Real-world policies rarely achieve this perfect benchmark because measurement, enforcement, and other distortions introduce gaps, but it serves as the theoretical standard. The other ideas miss this precise alignment or rely on unrealistic assumptions like no intervention or maximally high taxes.