Option 1 -> Marginal Product measures the change in output per unit change in one input, keeping others constant.
Option 2 -> Average Product is total output divided by the quantity of input used, not the change in output.
Option 3 -> Total Product is the total quantity of output produced, not the rate of change.
Option 4 -> Returns to Scale measures output changes when ALL inputs change proportionally, not one input.
Hence, Option 1: Marginal Product -> Marginal Product (MP) is a fundamental concept in production theory that measures the additional output generated by adding one more unit of a variable input while holding all other inputs constant. For example, if adding one more worker increases output by 10 units, the marginal product of labor is 10. This concept helps firms determine optimal input usage and follows the law of diminishing marginal returns. -> correct