In marginal analysis, the socially optimal quantity is reached when the marginal _____ equals the marginal social benefit.

In marginal analysis, the socially optimal quantity is reached when the marginal cost equals the marginal social benefit. This means that the cost of producing one more unit of a good or service is the same as the benefit that society receives from that unit. For example, if a factory produces one more car, the cost to the factory should equal the value that car brings to consumers and society as a whole. When these two values match, it indicates that resources are being used efficiently, and we are maximizing overall happiness and welfare. If the marginal cost is higher than the marginal social benefit, it suggests that producing more would actually harm society rather than help it.