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: Concept The halogens show a clear trend in physical state going down the group. This happens because the van der Waals (London dispersion) forces between the diatomic molecules get stronger as the molecules get larger and have more electrons.

| Halogen | Formula | State at room temperature | |---|---|---| | Fluorine | F₂ | Pale yellow gas | | Chlorine | Cl₂ | Greenish-yellow gas | | Bromine | Br₂ | Reddish-brown liquid | | Iodine | I₂ | Dark grey/black solid (sublimes to a purple vapour) |

Step 3: Check each option

• A. Iodine: a solid, so it is not correct.
• B. Chlorine: a gas, so it is not correct.
• C. Bromine: a liquid, so it is correct. Its melting point is about -7°C and its boiling point is about 59°C, so at room temperature it is a liquid.
• D. Fluorine: a gas, so it is not correct.

Step 4: Answer The correct option is C. Bromine.

Exam tip: Remember the order "Fluorine and Chlorine are Gases, Bromine is a Liquid, Iodine is a Solid". You can use the phrase "Go Get Little Sugar" for F, Cl, Br, I. Also remember that bromine is one of only two elements that are liquid at room temperature (the other is mercury, a metal).