In an externality graph illustrating pollution from copper production, what is the primary reason for the divergence between marginal private cost and marginal social cost?

In an externality graph showing pollution from copper production, the main reason for the difference between marginal private cost and marginal social cost is that the private cost only considers the expenses incurred by the producer. However, the social cost includes both the private costs and the additional costs that society faces due to pollution, like health problems and environmental damage. For example, if a copper factory produces metal at a cost of $100, but the pollution it creates leads to $50 in health care costs for nearby residents, the marginal social cost would be $150. This gap shows how the producer does not take full responsibility for the negative effects of their production, leading to overproduction of copper. Understanding this difference helps policymakers decide how to address these external costs, like through taxes or regulations.