Based on standard practices, the socially optimal quantity of pollution is "the quantity whose marginal social cost equals the marginal social benefit."
The socially optimal quantity is the term used to describe output quantity that reveals equilibrium between the costs and benefits of social conditions.
Therefore when the quantity of pollution whose marginal social cost equals the marginal social benefit occurs, this is a socially optimal quantity of pollution.
Hence, in this case, it is concluded that the correct answer is the quantity whose marginal social cost equals the marginal social benefit.
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