Consider a non-rivalrous good, like national defence, provided by the government. At the socially optimal level of provision of this good, the marginal
◦ cost of production of this good is zero.
◦ sacrifice society needs to make to supply the last unit of the good is equal to each consumer's marginal willingness to pay.
◦ cost of production of the last unit of the good is less than the consumers' marginal willingness to pay.
◦ cost of production of the last unit of the good is more than all consumers' combined marginal willingness to pay.
◦ marginal cost of production of the last unit of the good is equal to all consumers' combined marginal willingness to pay.