• Ultrasonic Membrane Cleaning Frequency:
• Acoustic Cavitation Mechanics:
• Power ultrasound de-fouls filtration membranes (UF/RO) by inducing acoustic cavitation—microscopic bubble formation and violent collapse producing localized shock waves and high-velocity microjets that dislodge foulant foul cakes.
• Operates in the low-frequency power ultrasound regime of $20 - 40\text{ kHz}$.
• Conclusion: 20-40 KHz (Option 2).

Correct option: (2) 20-40 KHz

• Operating Pressures in High Pressure Processing (HPP):
• Commercial Parameters:
• High Pressure Processing (pascalization / cold isostatic pressing) subjects hermetically packaged foods submerged in water to pressures between 100 and 800 MPa ($1,000 - 8,000\text{ bar}$ or $14,500 - 116,000\text{ psi}$).
• Most commercial food cycles operate between $400$ and $600\text{ MPa}$ with dwell times of $2 - 5\text{ minutes}$ to inactivate vegetative pathogens and spoilage enzymes without heat.
• Conclusion: 100 to 800 MPa (Option 2).

Correct option: (2) 100 to 800 MPa

• Non-Invasive Ultrasonic Characterization of Food Viscoelasticity:
• Low-Intensity Ultrasound Diagnostics:
• Measures acoustic wave velocity and attenuation coefficient ($\gt 100\text{ kHz}$) propagating through food specimens.
• Provides non-destructive, non-invasive measurement of dynamic storage modulus ($G'$), loss modulus ($G''$), and complex viscoelastic rheology in real time.
• Conclusion: Ultrasound (Option 3).

Correct option: (3) Ultrasound