Which type of goods are typically under-provided in a free market due to non-excludability?

The correct choice is public goods, which are characterized by two main features: non-excludability and non-rivalry. Non-excludability means that once these goods are provided, it is difficult or impossible to prevent anyone from using them. Non-rivalry implies that one person's use of a public good does not reduce its availability for others.

Due to these characteristics, public goods tend to be under-provided in a free market. Individuals may avoid paying for public goods because they can benefit from them without contributing to their cost, leading to the "free rider problem." This results in insufficient investment by private entities, leaving these goods under-provided when compared to the socially optimal level.

In contrast, private goods are excludable and rivalrous, meaning they are sold in markets where individuals have to pay for them, which incentivizes their production. Common resources, while non-excludable, are rivalrous and can lead to over-exploitation rather than under-provision. Collective goods is a broader classification that may include public goods, but the term isn't used in economic theory as specifically as public goods are. Therefore, the distinction of public goods being under-provided due to their inherent characteristics is what makes this choice accurate.