# Concentrated hydrochloric acid when kept in open air sometimes produces a cloud of white fumes. The explanation for it is that Option 1) concentrated hydrochloric acid emits strongly smelling $HCl$  gas all the time Option 2) oxygen in air reacts with the emitted $HCl$ gas to form a cloud of chlorine gas Option 3) strong affinity of $HCl$ gas for moisture in air results in forming of droplets of liquid solution which appears like a cloudy smoke Option 4) due to strong affinity for water, concentrated hydrochloric acid pulls moisture of air towards itself. This moisture forms droplets of water and hence the cloud.

As we learnt in

Deacon process -

$2HCl+\frac{1}{2}O_{2} \xrightarrow[]{CuCl_{2}}Cl_{2}+H_{2}O$

- wherein

CuCl2 used as catalyst

Concentrated HCl produces vapours of HCl. As HCl has strong affinity for moisture, it yields the formation of droplets of liquid solution which appear like a cloudy smoke.

Option 1)

concentrated hydrochloric acid emits strongly smelling $HCl$  gas all the time

This option is incorrect.

Option 2)

oxygen in air reacts with the emitted $HCl$ gas to form a cloud of chlorine gas

This option is incorrect.

Option 3)

strong affinity of $HCl$ gas for moisture in air results in forming of droplets of liquid solution which appears like a cloudy smoke

This option is correct.

Option 4)

due to strong affinity for water, concentrated hydrochloric acid pulls moisture of air towards itself. This moisture forms droplets of water and hence the cloud.

This option is incorrect.

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