Read the passage carefully and answer the questions based on the passage:

Law of Variable Proportion and Return to Scale.

The law of variable proportions arises because factor proportions change as long as one factor is held constant and the other is increased. What if both factors can change? Remember that this can happen only in the long run. When a proportional increase in all inputs results in an increase in output by the same proportion, the production function is said to display Constant returns to scale (CRS).

When a proportional increase in all inputs results in an increase in output by a larger proportion, the production function is said to display Increasing Returns to Scale (IRS). Decreasing Returns to Scale (DRS) holds when a proportional increase in all inputs results in an increase in output by a smaller proportion.

The core reason behind the arising law of variable proportion is........

Factor proportion changes with keeping one factor constant.

The correct answer is Option (1) → Factor proportion changes with keeping one factor constant.

The passage states: "The law of variable proportions arises because factor proportions change as long as one factor is held constant and the other is increased."

The Law of Variable Proportions (also known as the law of diminishing marginal product) is a short-run concept in production theory. It explains how output changes when one input is varied while all other inputs are kept constant. The core reason this law arises is the fixity of at least one factor of production. When some factors are fixed (like land or capital in the short run) and variable factors (like labor) are continuously increased, the proportion in which factors are combined changes. Initially, the fixed factor might be underutilized, and adding more units of the variable factor leads to increasing returns. However, beyond a certain point, the fixed factor becomes increasingly overutilized relative to the variable factor. This leads to diminishing returns, as additional units of the variable input have less and less of the fixed input to work with, causing their marginal contribution to production to decline.