Option 1 -> Marginal rate of substitution relates to consumer preferences and indifference curves, not production possibilities.
Option 2 -> Marginal rate of transformation is the rate at which one good must be given up to produce another good.
Option 3 -> Marginal rate of exchange is not the standard term used for PPC slope.
Option 4 -> Opportunity cost is represented by the slope but is not the technical term for it.
Hence, Marginal rate of Transformation -> The slope of the Production Possibility Curve (PPC) is technically called the Marginal Rate of Transformation (MRT). It measures the rate at which the production of one good can be transformed into another by reallocating resources. The MRT equals the opportunity cost of producing one additional unit of a good in terms of the other good forgone. For example, if the MRT is 2, it means 2 units of Good Y must be sacrificed to produce 1 additional unit of Good X. -> correct