The marginal product of an input initially rises and then after a certain level of employment, it starts falling, thus MP curve looks like an inverse 'U'- shaped curve. This condition is under ............

Option 1 -> Refers to long-run where output increases proportionately less than increase in all inputs.

Option 2 -> Describes short-run production where one input is fixed and MP of variable input first rises then falls, creating inverse U-shaped curve.

Option 3 -> Refers to long-run where output increases proportionately more than increase in all inputs.

Option 4 -> Refers to long-run where output increases proportionately equal to increase in all inputs.

Hence, Option 2: Law of Variable Proportions -> This law operates in the short-run when at least one factor of production is fixed while others are variable. As we keep increasing the variable input (keeping fixed input constant), the marginal product initially increases due to better utilization of fixed factor (Stage I - Increasing Returns), then starts declining due to overcrowding of variable factor over fixed factor (Stage II - Diminishing Returns), and may even become negative (Stage III). This creates the characteristic inverse U-shaped MP curve described in the question. Returns to Scale concepts (options 1, 3, 4) apply to long-run when all inputs are variable and don't exhibit this inverse U-shaped pattern. -> correct