Which of the following elements is an inert noble gas?

Introduction / Context:
Inert gases, also called noble gases, are elements in group 18 of the periodic table that show very low chemical reactivity under normal conditions. They are commonly used in lighting, welding, and as protective atmospheres. This question tests whether the learner can recognise one such gas among familiar atmospheric components.

Given Data / Assumptions:

• Candidates listed are hydrogen, nitrogen, oxygen, and argon.
• Inert gases are noble gases such as helium, neon, argon, krypton, xenon, and radon.
• We assume standard periodic table groupings.

Concept / Approach:
Noble gases have completely filled valence electron shells, making them chemically stable. Argon, with atomic number 18, has a full outer shell and belongs to group 18. In contrast, hydrogen (group 1), nitrogen (group 15), and oxygen (group 16) are reactive non metals that form many compounds. Therefore, we identify which of the options is in group 18 and hence inert.

Step-by-Step Solution:
Step 1: Recall the list of noble gases. Helium, neon, argon, krypton, xenon, and radon are noble gases. Step 2: Compare this list with the given options. Among hydrogen, nitrogen, oxygen, and argon, only argon appears in the noble gas list. Step 3: Conclude that argon is the inert gas in the given set.

Verification / Alternative Check:
Looking at the periodic table, argon is in group 18, period 3. Its electron configuration ends with 3s2 3p6, indicating a complete octet. Hydrogen has a single electron and is reactive, nitrogen forms nitrates, ammonia, and other compounds, and oxygen participates in combustion and respiration reactions. Only argon remains largely unreactive under ordinary conditions, confirming our choice.

Why Other Options Are Wrong:
Option A: Hydrogen is reactive and forms many compounds, such as water and acids. It is not a noble gas. Option B: Nitrogen, although relatively less reactive at room temperature due to a strong triple bond in N2, can form many compounds and is not classified as a noble gas. Option C: Oxygen is a very reactive element that supports combustion and is essential for respiration, not an inert gas.

Common Pitfalls:
Sometimes students confuse low reactivity with complete inertness and may think nitrogen is inert simply because air is mostly nitrogen and it does not catch fire easily. However, the term inert gas in the periodic table context refers specifically to group 18 noble gases. Keeping this distinction clear helps to avoid mixing up nitrogen and noble gases.

Final Answer:
The inert noble gas among the options is Argon.