• Terminal Velocity in Aerodynamic Separation:
• In seed cleaners and combine harvester winnowing systems, pneumatic separation relies on differences in terminal velocity ($v_t$):
• Clean wheat grain has a terminal velocity of 9.0 – 11.5 m/s.
• Wheat weed seeds and broken kernels: 5.0 – 8.0 m/s.
• Wheat chaff (bhusa / glumes) is light and airy, having a terminal velocity of 1.5 – 2.5 m/s.
• Maintaining air blast velocity between 3.0 and 7.0 m/s cleanly blows away chaff ($v_t = 1.5 - 2.5$ m/s) while allowing grain to fall.
• Conclusion: 1.5 - 2.5 m/s (Option 1).

Correct option: (1) 15-25ms7*