The reduction ratio for fine grinders is

Why is RR high for fine grinders?
Because:

Feed size is often several millimeters (e.g., 5–10 mm)

Product size is extremely small (e.g., 50 microns = 0.05 mm)

Reduction Ratio
=
5
 mm
0.05
 mm
=
100
Reduction Ratio=
0.05 mm
5 mm
​
=100
Thus, RR can go as high as 100 or even more depending on how fine the final product is.

📘 Standard Book Support:
From McCabe, Smith & Harriott (Unit Operations of Chemical Engineering):

"For fine grinders, reduction ratios are very high, typically up to 100, due to the very small particle size required."

✅ Final Answer:
D. As high as 100