When chlorine water is exposed to bright sunlight, the following products are formed

Analyze the question: Chlorine water is Cl₂ dissolved in water. It contains HCl and HOCl (hypochlorous acid). We need the products when it is exposed to bright sunlight.

Concept: Chlorine dissolves in water and reacts reversibly:

Cl₂ + H₂O ⇌ HCl + HOCl

Hypochlorous acid is unstable. In bright sunlight (ultraviolet light) it decomposes, releasing oxygen:

2HOCl → 2HCl + O₂

Step-by-step solution:

1. Chlorine water first forms HCl and HOCl: Cl₂ + H₂O → HCl + HOCl
2. Sunlight decomposes HOCl: 2HOCl → 2HCl + O₂
3. Overall equation: 2Cl₂ + 2H₂O → 4HCl + O₂ (in sunlight)

So the final products are hydrochloric acid and oxygen gas. This is why bottles of chlorine water are kept in dark or brown bottles. The bubbles you see in a bottle of chlorine water left in the sun are oxygen. The solution also loses its bleaching power, because the HOCl (the bleaching agent) is used up, and it becomes more acidic because of the extra HCl.

Checking the options:

• A: Cl₂ is the starting material, not a product, and no oxygen is released. Wrong.
• B: HOCl is what breaks down, so it will not remain. Wrong.
• C: HCl(aq) and O₂ match the decomposition. Correct.
• D: HOCl is decomposed, so it is not a final product. Wrong.

Answer: C. HCl(aq) and O₂

Exam tip: Remember "sunlight kills HOCl": HOCl → HCl + O₂. Whenever you see chlorine water and sunlight together, think oxygen gas and HCl.