Step 1: Understanding the Concept:
This question asks for the term that defines the performance or efficiency of a screening operation. Screening is a mechanical process used to separate a mixture of particles into different size fractions.
Step 2: Detailed Explanation:
Let's define the terms in the options:
(A) Ideal screen: An ideal screen is a theoretical concept where the separation is perfect. All particles larger than the screen opening (aperture) go to the overflow (oversize fraction), and all particles smaller than the opening go to the underflow (undersize fraction). Real screens are never ideal.
(B) Screen effectiveness (or Screen efficiency): This is a quantitative measure of how well a real screen performs compared to an ideal screen. It represents the ability of the screen to successfully separate the feed material into the desired overflow (coarse) and underflow (fine) fractions. It is calculated based on the mass fractions of the desired and undesired material in the output streams. This term precisely matches the description in the question.
(C) Rotary screen: This is a specific {type} of screening equipment (a rotating cylindrical screen), not a measure of performance.
(D) Screening: This is the name of the overall {process} of size separation using a screen, not the measure of its ability.
Step 3: Final Answer:
The ability of a screen to separate feed based on size is quantified by its effectiveness or efficiency. Therefore, option (B) is the correct answer.