Which is a gas at room temperature?
A) aluminum
B) nitrogen
C) potassium
D) sodium
The Correct Answer and Explanation is:
The correct answer is B) nitrogen.
At room temperature, nitrogen is a gas, while aluminum, potassium, and sodium are metals that exist in solid form under the same conditions. To understand why nitrogen is a gas at room temperature while the others are solid, we must consider the atomic and molecular structure of these elements and their bonding properties.
Nitrogen (N)
Nitrogen is a diatomic molecule, meaning it exists as two nitrogen atoms (N₂) bonded together by a triple covalent bond. The molecular structure of nitrogen gives it low boiling and melting points because the intermolecular forces (Van der Waals forces) between nitrogen molecules are weak. Nitrogen gas remains stable at room temperature, which is around 20°C (68°F), because the energy in the environment is insufficient to overcome the strong covalent bonds within the nitrogen molecules. As a result, nitrogen remains in its gaseous form, which is characteristic of many non-metallic elements with small molecules.
Aluminum (Al)
Aluminum is a metal with a crystalline structure at room temperature. It has a high melting point (660°C) due to the strong metallic bonds between its atoms. These bonds involve a “sea” of delocalized electrons, which allows aluminum to conduct electricity and heat well. The strong bonding also keeps aluminum in its solid state at room temperature.
Potassium (K) and Sodium (Na)
Both potassium and sodium are alkali metals, which are also solid at room temperature. While they have relatively low melting points compared to other metals (63.5°C for potassium and 97.8°C for sodium), they are still well above room temperature. Alkali metals are soft, reactive solids that can conduct electricity, but their metallic bonds keep them in solid form until heated beyond their melting points.
Thus, nitrogen’s gaseous state at room temperature differentiates it from the other elements in the list.