Chlorine displaces bromine from aqueous potassium bromide because

Step 1: Analyze the question The question asks why chlorine can displace bromine from potassium bromide solution. This is a halogen displacement reaction.

Step 2: The concept Within Group 17 (the halogens), reactivity decreases down the group: F > Cl > Br > I. A more reactive halogen displaces a less reactive halogen from its salt solution. Reactivity here means the ability to gain electrons, which is the strength as an oxidising agent.

Step 3: The solution The reaction is:

Cl₂(g) + 2KBr(aq) → 2KCl(aq) + Br₂(l)

In ionic form:

Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

• Chlorine gains electrons: Cl₂ + 2e⁻ → 2Cl⁻ (reduction), so chlorine is the oxidising agent.
• Bromide ions lose electrons: 2Br⁻ → Br₂ + 2e⁻ (oxidation).

Chlorine is a stronger oxidising agent because it is a smaller atom. Its nucleus attracts incoming electrons more strongly, so it gains electrons more readily than bromine does. The solution turns orange or brown as free bromine forms.

Step 4: Checking the options

• A. Physical state does not decide whether displacement occurs. ✗
• B. Bromine being weakly acidic is irrelevant. ✗
• C. Bromine does have a larger atomic radius than chlorine, which is part of why it is less reactive. But this is a fact about size, not the direct reason for displacement. The direct reason is the difference in oxidising power. ✗
• D. Chlorine is a stronger oxidising agent than bromine. ✓ This is the direct reason.
• E. Density has no bearing on reactivity. ✗

Answer: D

Tip: For displacement questions, remember "the stronger oxidising agent takes the electrons." In the halogens, oxidising power falls down the group, so Cl₂ will displace Br₂ and I₂, and Br₂ will displace I₂, but never the other way round.