Vapour-phase chemical disinfectants: Identify which agents are used in the vapour or gas phase for high-level disinfection or sterilization of spaces and equipment.

Introduction / Context:
Some chemical agents are applied as vapours or gases to decontaminate rooms, cabinets, porous materials, or packaged devices. Recognizing which chemicals function effectively in the vapour phase is crucial for selecting methods that penetrate and achieve high-level microbial kill.

Given Data / Assumptions:

• Fumigation and gas sterilization require volatility and proven microbicidal activity.
• Penetration into porous surfaces and complex equipment is essential.
• Safety controls and aeration are required due to toxicity.

Concept / Approach:
Formaldehyde gas (historically from formalin evaporation) has been used to fumigate rooms and biosafety cabinets, achieving broad-spectrum kill (now often replaced by safer agents). Ethylene oxide is a widely used gaseous sterilant for heat- and moisture-sensitive devices, with deep penetration and sporicidal action. Both are classic examples of vapour-phase disinfectants/sterilants.

Step-by-Step Solution:
1) List volatile microbicides used as gas: formaldehyde and EtO.2) Confirm their spectrum: bactericidal, fungicidal, virucidal, and sporicidal with adequate exposure.3) Recognize application contexts: room/cabinet fumigation (formaldehyde); device sterilization (EtO).4) Choose the combined option as correct.

Verification / Alternative check:
Institutional protocols document historical formaldehyde fumigation and ongoing EtO sterilization programs for complex medical devices, affirming their vapour-phase roles.

Why Other Options Are Wrong:

• Formaldehyde or EtO alone: each is correct but the question asks for identification including both.
• None of these: incorrect because both are valid.
• Glutaraldehyde mist: glutaraldehyde is a liquid high-level disinfectant used by immersion; aerosolization is not standard or safe as a vapour-phase sterilant.

Common Pitfalls:
Confusing liquid immersion disinfectants with vapour or gas sterilants; underestimating the need for aeration and monitoring after gas use.

Final Answer:
Both (a) and (b).