Which of the following halogens is liquid at room temperature?

Step 1: Analyze the question We need the halogen (Group 17 element) that exists as a liquid at room temperature (about 25 °C).

Step 2: Explain the concept Halogens show a clear trend in physical state going down the group. This is because the intermolecular forces (van der Waals/London forces) get stronger as the molecules get larger and have more electrons. Stronger forces mean higher melting and boiling points.

| Halogen | Physical state at room temperature | |---|---| | Fluorine (F₂) | Pale yellow gas | | Chlorine (Cl₂) | Greenish-yellow gas | | Bromine (Br₂) | Reddish-brown liquid | | Iodine (I₂) | Shiny dark-grey/purple solid |

Step 3: Apply to the options

• A. Chlorine is a gas. ❌
• B. Fluorine is a gas. ❌
• C. Iodine is a solid (it sublimes on heating to give purple vapour). ❌
• D. Bromine is a reddish-brown volatile liquid. ✅

Bromine is also one of only two elements that are liquid at room temperature and standard pressure. The other is mercury, a metal.

Answer: D. Bromine

Exam tip: Remember the order "Gas, Gas, Liquid, Solid" for F, Cl, Br, I. You can also remember that Bromine is the Blood-red/brown Boy that is a liquid, as both start with "B" for the "liquid in the middle." The colours darken down the group too: pale yellow → greenish-yellow → reddish-brown → purple-black.