Unit operations check — pick the wrong statement:\nWhich of the following statements about separation and crushing/screening equipment is incorrect in standard chemical engineering practice?

Introduction / Context:
This item tests basic vocabulary used in particle technology: magnetic separation modes, the definition of reduction ratio, the role of a gyratory crusher, and common screen motions. Getting these definitions correct is essential for flowsheet reading and quick equipment selection during preliminary design.

Given Data / Assumptions:

• Conventional mineral/chemical processing definitions apply.
• Reduction ratio refers to a single crushing stage.
• “Gyratory crusher” implies the large primary machine used ahead of secondary/tertiary stages.

Concept / Approach:
Magnetic separators are indeed used in both dry and wet duty. Gyratory crushers are the classic primary coarse crushers. Screens can be stationary (grizzlies), moving/gyratory, or vibratory (linear/circular). The only problematic statement is the definition of reduction ratio: it is correctly defined as characteristic feed size divided by characteristic product size (e.g., F80/P80 or feed opening/product opening). The option given inverts and also misstates it (“minimum feed” over “maximum product”).

Step-by-Step Solution:

Verification / Alternative check:
Handbooks define R using F80 and P80 (or nominal openings), never “minimum feed” over “maximum product,” which would contradict observed capacity trends.

Why Other Options Are Wrong:

• (a) Correct: magnetic separation is used for both dry and wet ore processing.
• (c) Correct: gyratories are coarse/primary crushers.
• (d) Correct: all listed screen motions are widely used.

Common Pitfalls:
Confusing “openings” with statistical sizes (F80/P80); always state which sizes are used.

Final Answer:
Reduction ratio in crushing is the ratio of minimum feed size to maximum product size.