Which chemical is known to exhibit the most dangerous properties without proper storage?

Perchloric acid is considered to exhibit the most dangerous properties without proper storage primarily due to its strong oxidizing properties, especially when it comes into contact with organic materials or other incompatible substances. When it is improperly stored, perchloric acid can lead to violent reactions, potentially resulting in explosions or the release of toxic gases. It is also highly reactive, and even minor impurities can exacerbate its reactivity.

In contrast, while sodium hydroxide, hydrochloric acid, and acetone also have hazardous characteristics, they do not share the same level of explosiveness or propensity for violent reactions as perchloric acid does. Sodium hydroxide is a strong base and can cause severe chemical burns, while hydrochloric acid is a strong acid that can release corrosive fumes but lacks the same oxidizing danger. Acetone is a flammable solvent, but it does not exhibit the dangerous oxidizing nature of perchloric acid. Thus, proper storage, which involves keeping perchloric acid away from organic materials and in designated containers, is essential to prevent hazardous situations.