Problem 25 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is an inert gas? (a) \(\mathrm{O}_{2}\) (b) argon (c) \(\mathrm{N}_{2}\) (d) \(\mathrm{H}_{2}\)

Step-by-Step Solution

Answer

Argon is an inert gas.

Step 1: Understand What 'Inert Gas' Means

Inert gases are also known as noble gases. These gases are characterized by having very low chemical reactivity due to their full valence electron shells. They are in Group 18 of the periodic table.

Step 2: Identify Noble Gases

List the noble gases. They are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These elements are known for their stability and low reactivity.

Step 3: Evaluate Each Option

Compare each given option with the list of noble gases from Step 2: - (a)     (Oxygen:  not an inert gas) - (b) Argon:  is a noble gas - (c)        (Nitrogen:  not   ) - (d)    (Hydrogen:   )

Step 4: Confirm the Answer

Since argon is on the list of noble gases and matches with one of the options, it is confirmed as an inert gas. Meanwhile, oxygen and nitrogen are both gases, but they are not inert gases. Hydrogen is also not considered an inert gas.

Key Concepts

Noble Gases

Noble gases, also referred to as inert gases, are a group of chemical elements with similar properties that are found in Group 18 of the periodic table. These gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Their defining characteristic is the full valence electron shell, which typically makes them extremely stable and unreactive under most conditions.

Their stability arises from having the ideal electron configuration, meaning they have no incentive to gain or lose electrons. This lack of reactivity is why they are termed "inert." For instance:

• Helium, with its two electrons, maintains a complete outer shell.
• Neon and argon also have filled valence shells, which is typical for noble gases.

They are used in various fields, such as in lighting and as non-reactive blankets in chemical reactions.

Argon

Argon is a noble gas, and it is the third most abundant gas in Earth's atmosphere, following nitrogen and oxygen. It makes up approximately 0.93% of the atmosphere. Due to its inert nature, argon does not readily form compounds under normal circumstances, allowing it to provide a stable environment where reactions are undesired.

In practical applications, argon is used:

• In welding to shield heated metals from contamination by reactive elements like oxygen.
• As a filler gas in incandescent and fluorescent light bulbs to prevent oxidation of the filament.
• In double-glazed windows for enhanced insulation.

Its non-reactive properties make it ideal for preserving old documents and materials that need protection from deterioration.

Periodic Table

The periodic table is a structured arrangement of all known chemical elements. It organizes elements based on their atomic number, electron configuration, and recurring chemical properties. Dmitri Mendeleev first developed this much-used tool in the 19th century.

Elements are placed in rows called periods and columns known as groups, with the noble gases residing at the far right in Group 18. This placement reflects their full valence shells:

• Each element across a period has one more proton and is less metallic than the previous one.
• Each group consists of elements with similar chemical behaviors.

The periodic table is fundamental in understanding chemical reactions and properties of elements, acting as a visual guide for students and scientists alike.

Chemical Reactivity

Chemical reactivity refers to the tendency of a substance to engage in chemical reactions. This involves breaking chemical bonds in reactants and forming new ones in products. Atoms and molecules react to achieve a more stable electronic configuration, often resembling the noble gases.

Reactivity varies among elements due to:

• Electron configurations, which influence whether an element will gain, lose, or share electrons in a reaction.
• The presence of incomplete valence electron shells, which drive reactivity as elements seek stability.

Noble gases represent the least reactive elements due to their complete electron shells. This stability makes them unique, in contrast to highly reactive groups such as the alkali metals and halogens, which tend to readily form compounds.