Analyzing Common Characteristics of Gases

Let's carefully examine the characteristics of hydrogen (\(H_2\)), nitrogen (\(N_2\)), oxygen (\(O_2\)), and carbon dioxide (\(CO_2\)) based on the given options to find what they have in common.

Examining Option 1: Are They All Diatomic?

• Hydrogen (\(H_2\)) molecule consists of two hydrogen atoms, so it is diatomic.
• Nitrogen (\(N_2\)) molecule consists of two nitrogen atoms, so it is diatomic.
• Oxygen (\(O_2\)) molecule consists of two oxygen atoms, so it is diatomic.
• Carbon dioxide (\(CO_2\)) molecule consists of one carbon atom and two oxygen atoms, making it triatomic.

Since carbon dioxide (\(CO_2\)) is not diatomic, this characteristic is not common to all four substances.

Examining Option 2: Are They All Gases at Room Temperature?

Room temperature is generally considered to be around \(20-25^\circ C\). Let's look at the state of each substance at room temperature:

• Hydrogen (\(H_2\)) is a gas at room temperature.
• Nitrogen (\(N_2\)) is a gas at room temperature.
• Oxygen (\(O_2\)) is a gas at room temperature.
• Carbon dioxide (\(CO_2\)) is a gas at room temperature and standard pressure.

This characteristic is common to all four substances.

Examining Option 3: Are They All Colored?

• Hydrogen (\(H_2\)) is a colorless gas.
• Nitrogen (\(N_2\)) is a colorless gas.
• Oxygen (\(O_2\)) is a colorless gas (although liquid oxygen is pale blue).
• Carbon dioxide (\(CO_2\)) is a colorless gas.

None of these gases are colored at room temperature, so this characteristic is not common to all four substances.

Examining Option 4: Do They All Have Same Reactivity?

The reactivity of these gases varies significantly:

• Hydrogen (\(H_2\)) is flammable and relatively reactive, especially with oxygen.
• Nitrogen (\(N_2\)) is a very unreactive gas due to the strong triple bond between the nitrogen atoms.
• Oxygen (\(O_2\)) is highly reactive and supports combustion.
• Carbon dioxide (\(CO_2\)) is relatively unreactive, especially at room temperature, often used as a fire extinguisher.

They clearly have different reactivities, so this characteristic is not common to all four substances.

Conclusion

Based on the analysis of each option, the only characteristic common to hydrogen, nitrogen, oxygen, and carbon dioxide among the choices provided is that they are all gases at room temperature.

Revision Table: Properties of Selected Gases

Additional Information: States of Matter and Molecular Structure

The state of a substance (solid, liquid, or gas) at a given temperature and pressure depends on its intermolecular forces and the kinetic energy of its particles. For many common substances like \(H_2\), \(N_2\), \(O_2\), and \(CO_2\), their boiling points are below room temperature, which is why they exist as gases under standard conditions.

The term 'diatomic' refers to a molecule made up of two atoms. Elements like hydrogen, nitrogen, oxygen, fluorine (\(F_2\)), chlorine (\(Cl_2\)), bromine (\(Br_2\)), and iodine (\(I_2\)) naturally exist as diatomic molecules. Molecules made of more than two atoms, like \(CO_2\) (three atoms), are called polyatomic molecules.