Which of the following halogens is solid at room temperature?

Step 1: Analyze the question You are asked to identify which halogen is a solid at room temperature (about 25°C).

Step 2: Concept - physical states of the halogens (Group 17) The halogens change state as you go down the group. This is because the molecules (X₂) get bigger, so the van der Waals (intermolecular) forces get stronger, and more energy is needed to separate the molecules.

| Halogen | State at room temperature | Colour | |---|---|---| | Fluorine (F₂) | Gas | Pale yellow | | Chlorine (Cl₂) | Gas | Greenish-yellow | | Bromine (Br₂) | Liquid | Reddish-brown | | Iodine (I₂) | Solid | Dark grey/black (purple vapour) |

Step 3: Apply to the options

• A. Bromine is a liquid, so it is not correct.
• B. Chlorine is a gas, so it is not correct.
• C. Fluorine is a gas, so it is not correct.
• D. Iodine is a solid, so it is correct.

Answer: D. Iodine

Tip: Remember the trend "Go Get Lunch Soon": Gas (F, Cl), Liquid (Br), Solid (I). Also, iodine sublimes, turning directly from a solid to a purple vapour when heated. This is a favourite follow-up question in WASSCE and JAMB.