Which of these designates a gas at room temperature?

`"HCl"(g)`, as `"HCl"` is naturally a gas at room temperature and pressure. It boils below room temperature, at `-85.05^@ "C"`.

The way you can figure out what you're looking at is by looking at what is in parentheses:

• `(g) = "gas"`
• `(l) = "liquid"`, or very concentrated (high `"mol solute"/"L solution"`)
• `(s) = "solid"`, or precipitate if within a reaction

The above are all phases, though `(l)` can indicate a concentrated solution.

Anything else specifies a solvent that the solute dissolves in (or a liquid that another liquid mixes with to form a liquid-liquid mixture), which is another way of saying that it is a solution:

`B)` specifies bromine liquid (`"Br"_2(l)`) dissolved in liquid alcohol (bromine is a liquid at room temperature and pressure). An alcohol can be anything containing only `"C"` connected to `"H"` (a hydrocarbon end), and `"OH"` (a hydroxyl group), such as ethanol and butanol.

`C)` is sucrose (common sugar, `"C"_(11)"H"_(22)"O"_(11)`) dissolved in water. `(aq)` denotes an aqueous solution, which is by definition something dissolved in water.

`D)` is chlorine gas (`"Cl"_2(g)`) dissolved in carbon tetrachloride liquid (`"CCl"_4(l)`). Chlorine is a gas at room temperature (check that its boiling point is less than `25^@ "C"`), while `"CCl"_4` has a boiling point higher than `25^@ "C"`.