Which antifreeze solution is recommended as the first choice for protecting fixture traps against freezing?

Glycol is recommended as the first choice for protecting fixture traps against freezing because it has excellent antifreeze properties, which effectively lower the freezing point of water. This means that it can prevent water in pipes and fixture traps from freezing even in low temperatures. Glycol is commonly used in various applications due to its non-toxic nature when used in the right concentrations and its ability to provide reliable freeze protection without being corrosive to pipes and fixtures.

The other options, while having various properties, do not offer the same level of freeze protection or safety. Alcohol may work as an antifreeze but typically has a higher volatility and could pose more risks in terms of flammability and toxicity. Glycerin, though safe and non-toxic, does not perform as effectively as glycol in terms of lowering the freezing point and might present challenges regarding viscosity and flow in cold conditions. Calcium chloride is a strong desiccant and is typically used for other purposes, such as de-icing, but it can be corrosive to plumbing systems and is not suited for use in fixture traps. Thus, glycol stands out as the most appropriate choice for this application.