• Standard Tyler / US Sieve Series Aperture Sizes:
• Conversion Formula: Mesh number refers to the number of openings per linear inch ($25.4\text{ mm}$):

• Standard Values for Nematode Extraction Sieves:
• 20 mesh: $850\,\mu\text{m}$
• 60 mesh: $250\,\mu\text{m}$
• 100 mesh: $150\,\mu\text{m}$
• 200 mesh: $75\,\mu\text{m}$
• 300 mesh: $53\,\mu\text{m}$
• 350 mesh: $45\,\mu\text{m}$ (nominal standard aperture $44-45\,\mu\text{m}$)
• 400 mesh: $38\,\mu\text{m}$
• Conclusion: The aperture size of a 350 mesh sieve is $45\,\mu\text{m}$ (Option 2).

Correct option: (2) 45um