Answer:
the opportunity cost of the good measured on the horizontal axis.
Step-by-step explanation:
The Production possibilities frontiers is a curve that shows the various combination of two goods a company can produce when all its resources are fully utilised.
The PPF is concave to the origin. This means that as more quantities of a product is produced, the fewer resources it has available to produce another good. As a result, less of the other product would be produced. So, the opportunity cost of producing a good increase as more and more of that good is produced.