If a country decides to produce more of good X by reallocating resources from good Y, the opportunity cost is solely determined by the quantity of good Y that is no longer produced, without considering the potential alternatives for those resources.

When a country decides to produce more of good X instead of good Y, it has to take resources like labor and materials away from making good Y. The opportunity cost is the amount of good Y that is lost because those resources are now focused on good X. This means that the country must consider how much less of good Y they can produce when they shift their efforts. For example, if a factory that makes bicycles (good Y) is converted to make cars (good X), the opportunity cost is the number of bicycles that will not be produced. However, it's important to remember that opportunity cost also includes what else those resources could have been used for, not just the lost production of good Y.