The relationship between an increase in variable input and output when all other inputs are held constant is referred to as.

Marginal Product.

The correct answer is Option (3) → Marginal Product.

Marginal Product (MP) refers to the additional output produced when one more unit of a variable input (like labor) is added, while all other inputs are held constant. It shows the change in total product resulting from a change in the variable input, and is a key concept in the law of variable proportions.

Note: The given answer is correct and as per NTA/NCERT. Both Total Product and Marginal Product are related to the relationship between input and output, but the question specifically refers to the change in output due to change in input. Total Product (TP) shows the overall relationship between variable input and output. But the question clearly says “increase in variable input and output”, which means we are focusing on the additional/change in output, not the total level. That is exactly the definition of Marginal Product (MP):It measures change in output due to change in one unit of input, keeping other inputs constant. Therefore, the correct answer remains Marginal Product (Option 3).