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When concentrated hydrochloric acid is left exposed to the atmosphere, it may give off a white fuming cloud. This happens because

1. oxygen present in air reacts with the released HCl gas, producing a cloud of chlorine gas
2. HCl gas has a strong attraction for moisture in air, causing tiny droplets of acid solution to form and look like white smoke
3. because of its strong attraction for water, concentrated hydrochloric acid draws in atmospheric moisture, which condenses into water droplets and forms the cloud
4. concentrated hydrochloric acid continuously releases strongly smelling HCl gas

Correct answer: HCl gas has a strong attraction for moisture in air, causing tiny droplets of acid solution to form and look like white smoke

Solution

Concentrated HCl gives off HCl gas, which is strongly hygroscopic. The gas attracts water vapour from the air to form tiny droplets of hydrochloric acid that appear as white fumes.

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