Concentrated hydrochloric acid when kept in open air sometimes produces a cloud of white fumes. The explanation for it is that :

Options

A. oxygen in air reacts with the emitted HCl gas to form a cloud of chlorine gas
B. strong affinity of HCl gas for moisture in air results in forming of droplets of liquid solution which appears like a cloudy smoke
C. due to storng affinity for water, concentrated hydrochloric acid pulls moisture of air towards itself. This moisture forms droplets of water and hence the cloud
D. cocentrated hydrochloric acid emits strongly smelling HCl gas all the time

Answer

To solve the question regarding the production of white fumes when concentrated hydrochloric acid is kept in open air, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Situation**: Concentrated hydrochloric acid (HCl) is a strong acid that can release HCl gas when exposed to air.

2. **Identifying the Reaction**: When HCl gas is released into the air, it can react with oxygen (O₂) present in the atmosphere. The reaction can be represented as follows:
\[ 4 \text{HCl} + \text{O}_2 \rightarrow 2 \text{Cl}_2 + 2 \text{H}_2\text{O} \]
Here, chlorine gas (Cl₂) is produced along with water (H₂O).

3. **Balancing the Reaction**: The equation is balanced as shown above, indicating that 4 moles of HCl react with 1 mole of O₂ to produce 2 moles of Cl₂ and 2 moles of H₂O.

4. **Formation of White Fumes**: The white fumes observed are primarily due to the chlorine gas produced in the reaction. Chlorine gas can react with moisture in the air to form hydrochloric acid (HCl) and hypochlorous acid (HClO), which can appear as a white cloud.

5. **Conclusion**: The most appropriate explanation for the formation of white fumes when concentrated hydrochloric acid is kept in open air is that oxygen in the air reacts with the emitted HCl gas to form a cloud of chlorine gas.

### Final Answer:
The correct explanation is: **Oxygen in air reacts with the emitted HCl gas to form a cloud of chlorine gas.**