• Membrane Filter Sterilization (Cold Sterilization): In microbiological and phytopathological laboratory protocols, heat-labile liquids (such as antibiotic solutions, vitamins, growth regulators, and viral inocula) cannot be autoclaved.
• Standard Pore Size: They are sterilized by membrane filtration using cellulose acetate, nylon, or PES membrane filters with a standard nominal pore diameter of $0.22\,\mu\text{m}$ (commonly specified as $0.2\,\mu\text{m}$).
• Sterility Mechanism: A $0.2\,\mu\text{m}$ pore size physically excludes all vegetative bacterial cells (Brevundimonas diminuta is used as the standard validation challenge), fungi, and mycoplasmas while permitting aqueous solutions to pass through.
• Conclusion: Filters of $0.2\,\mu\text{m}$ pore size are normally used (Option 3).

Correct option: (3) 0.2 um

• Mounting Media in Diagnostic Mycology: The most widely utilized universal mounting and staining reagent for temporary microscopic mounts of fungal mycelia, conidiophores, and spores is Cotton blue in lactophenol (LPCB).
• Chemical Constituents and Functions:
• Phenol: Rapidly kills fungal hyphae and inactivates autolytic enzymes.
• Lactic acid: Preserves fungal cellular morphology and structures.
• Glycerol: Maintains an osmotic balance and prevents the mount from drying out.
• Cotton blue (Aniline blue): Acidic stain that binds intensely to fungal cell-wall chitin, staining hyphae and reproductive spores bright blue.
• Conclusion: Cotton blue in lactophenol is the standard mounting medium (Option 2).

Correct option: (2) Cotton blue in lacto-phenol