Question

why does marginal opportunity cost tend to rise

Answer 1

because less and less efficient resources are transferred each time and no resource is equally efficient for producing both the commodities

Answer 2

The term marginal cost refers to the opportunity cost is an economic term that analyzes the effect of producing one more additional unit of a good.

As you increase production of one good, the opportunity cost to product an additional good will increase.

This is because of law of increasing opportunity cost.