Concept:Marginal product becomes negative when the total product curve starts to fall.
Explanation:Marginal product is the extra output produced when one additional unit of input is employed.
It is measured by the slope of the total product curve at a given point.
When the total product curve is rising, marginal product is positive.
When the total product curve reaches its highest point, marginal product becomes zero.
When the total product curve begins to decline, marginal product turns negative.
At point S, the total product curve is sloping downward, meaning total output is decreasing as more input is added.
Therefore, at point S, the additional output is negative, so marginal product is negative.
At points P and Q, the total product curve is still increasing, so marginal product is positive there.
At point R, the curve is at its maximum, where marginal product is zero.
Hence, S is the only point where marginal product is negative.
Answer:The correct point is S, which corresponds to option B.
