Pick the wrong statement — cakes and explosive materials:\nIdentify the incorrect statement among the following about filtration cakes and crushing practice.

Introduction / Context:
This question mixes two topics: filtration cake behavior and safe comminution of sensitive materials. It checks whether you can spot a statement that contradicts widely accepted engineering safety practice, while also recalling how cake resistance behaves with pressure for compressible cakes.

Given Data / Assumptions:

• Compressible cakes compact with increasing pressure drop.
• Explosive/dusty materials require special handling to avoid ignition.
• Gyratory crushers are used in primary, coarse crushing.

Concept / Approach:
Safe handling dictates that explosives and impact-sensitive powders are processed wet whenever feasible to control dust and dissipate heat; dry grinding increases dust explosion risk and frictional heating. Thus, the statement that explosive materials are crushed by dry grinding is incorrect. Regarding cakes, for compressible cakes, voidage and specific cake resistance change with pressure; assuming them constant is invalid. Also, cake resistance depends on pressure drop for compressible cakes. However, the single most clearly wrong and safety-critical statement here is the claim about dry grinding of explosive materials.

Step-by-Step Solution:

Verification / Alternative check:
Process safety guidelines recommend inerting, wet milling, and dust control to mitigate explosion hazards during size reduction.

Why Other Options Are Wrong:

• (a) Not strictly true for compressible cakes (they change), but (c) is the clearly wrong and unsafe assertion.
• (b) For compressible cakes, resistance depends on pressure; again (c) is the definitive incorrect practice.
• (d) Correct by definition.

Common Pitfalls:
Focusing only on filtration theory and missing the obvious safety violation in (c).

Final Answer:
Crushing of explosive materials is carried out by dry grinding.