Which of the following statements about chlorine and iodine at room temperature is correct?

Step 1: Analyze the question You are asked about the physical states of chlorine (Cl₂) and iodine (I₂) at room temperature (about 25 °C).

Step 2: The concept Chlorine and iodine are both Group 17 elements (the halogens). Down the group, the molecules get larger and have more electrons. This strengthens the weak van der Waals (intermolecular) forces between them, so melting and boiling points rise. That is why the physical state changes as you go down the group:

| Halogen | State at room temperature | |---|---| | Fluorine | Pale yellow gas | | Chlorine | Greenish-yellow gas | | Bromine | Reddish-brown liquid | | Iodine | Dark grey/black solid (it sublimes to a purple vapour on heating) |

Step 3: Check each option

• A. Chlorine is a gas and iodine is a solid. This is correct.
• B. Chlorine is not a liquid, and iodine is not a gas at room temperature. Wrong.
• C. Iodine is not a gas at room temperature. Wrong.
• D. This reverses the real states. Wrong.

Step 4: Answer The correct option is A: chlorine is a gas and iodine is a solid.

Exam tip: Remember the states of the halogens with "Go Get Lots Sugar" for F (gas), Cl (gas), Br (liquid), I (solid). Also remember that bromine is the only liquid halogen, and that iodine sublimes. Both facts are often tested.