Final answer:
Among the options given, Oxygen (O₂) is the only element that is gaseous at room temperature. It is a diatomic molecule and remains in the gas phase under standard conditions of temperature and pressure. The correct answer is C) Oxygen (O₂)
Step-by-step explanation:
The student has asked which elements are gaseous at room temperature. Out of the options provided, the correct answer is C) Oxygen (O₂). At room temperature and atmospheric pressure, mercury (Hg) is a liquid and aluminum (Al) is a solid, while bromine (Br) is also a liquid but is often near its boiling point.
Oxygen, on the other hand, is a diatomic molecule (O₂) that exists as a gas under these conditions, along with other members of the diatomic gases such as nitrogen (N₂). Oxygen is one of the few elements that are naturally gaseous at room temperature, which also includes noble gases like helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), as well as other diatomic molecules like hydrogen (H₂), nitrogen (N₂), fluorine (F₂), and chlorine (Cl₂).