Problem 136 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statement is not correct? (1) the hybridization of \(\mathrm{Xe}\) in \(\mathrm{XeF}_{4}\) is \(\mathrm{sp}^{3} \mathrm{~d}^{2}\) (2) \(\mathrm{XeO}_{3}\) has four \(\sigma\) and four \(\pi\) bonds (3) liquid helium is used as cryogenic liquid (4) among noble gases, the occurrence (\% by weight) of argon is higher in air. (a) 1 and 2 (b) 2 and 3 (c) 2 only (d) 3 only

Step-by-Step Solution

Answer

Statement 2 is incorrect. Correct answer: (c) 2 only.

Step 1: Analyze Statement 1

The hybridization of \(\mathrm{Xe}\) in \(\mathrm{XeF}_4\) is \(\mathrm{sp}^3 \mathrm{d}^2\). Xenon tetrafluoride (\(\mathrm{XeF}_4\)) has 6 electron pairs around the central xenon atom: 4 bond pairs for \(\mathrm{Xe-F}\) bonds and 2 lone pairs, leading to \(\mathrm{sp}^3 \mathrm{d}^2\) hybridization. This statement is correct.

Step 2: Analyze Statement 2

\(\mathrm{XeO}_3\) has four \(\sigma\) bonds and four \(\pi\) bonds. \(\mathrm{XeO}_3\) is a molecule with 3 oxidizing bonds involving xenon and oxygen, each having one \(\sigma\) bond and one \(\pi\) bond, totaling 3 \(\sigma\) bonds and 3 \(\pi\) bonds. Therefore, it does not have four \(\sigma\) and four \(\pi\) bonds. This statement is incorrect.

Step 3: Analyze Statement 3

Liquid helium is used as a cryogenic liquid. Liquid helium is known to be used for very low temperature applications due to its extremely low boiling point. This statement is correct.

Step 4: Analyze Statement 4

Among noble gases, the occurrence (% by weight) of argon is higher in air. Argon is the most abundant noble gas in Earth's atmosphere, making this statement correct.

Step 5: Conclude Incorrect Statements

Statements from Step 2 are identified as incorrect. This suggests that option (c) "2 only" is the correct choice, as only statement 2 contains an error.

Key Concepts

XeF4 hybridization

Xenon tetrafluoride, denoted as \(\mathrm{XeF}_4\), is a compound featuring the noble gas xenon. Understanding the hybridization of xenon in \(\mathrm{XeF}_4\) is crucial for comprehending its molecular geometry. In \(\mathrm{XeF}_4\), xenon is surrounded by six electron pairs. These include four bonding pairs shared with fluorine atoms and two lone pairs. To accommodate these electron pairs, xenon undergoes \(\mathrm{sp}^3 \mathrm{d}^2\) hybridization. This hybridization explains why \(\mathrm{XeF}_4\) has a square planar shape, as the arrangement minimizes electron pair repulsion. To visualize, picture the electron pairs positioning themselves as far apart as possible in a three-dimensional space, which in this case results in a geometry similar to a flat square with the lone pairs above and below xenon.

Cryogenic liquids

Cryogenic liquids are substances that are used in very low temperature environments. They're typically kept at temperatures below about 123 K (or 230°C or 190°F). Among the various cryogenic liquids, liquid helium stands out due to its exceptionally low boiling point of 4.2 K.
These liquids are vital in numerous applications including:

• Helium is used for cooling superconducting magnets in MRI systems.
• They are integral in aerospace engineering for cooling fuel and conducting space simulations.
• In scientific research settings, they help achieve conditions not possible at room temperature.

Using liquid helium and other cryogenic substances facilitates technological and scientific advancements by enabling experiments and procedures that depend on very low temperatures.

Abundance of noble gases in air

Noble gases are a group of inert gases found in the Earth's atmosphere, which include helium, neon, argon, krypton, xenon, and radon. Among these, argon is the most abundant noble gas present in the air by weight. It comprises approximately 0.93% of the Earth's atmosphere. Why does argon stand out among noble gases in terms of abundance?

• Argon is produced as a byproduct of the decomposition of potassium-40.
• It is also generated through the cosmic ray fractionation of nuclear materials in the Earth's crust.

Due to its relative abundance, argon is commonly used in various industrial applications, such as in fluorescent lighting and welding, owing to its inert nature. This makes it a practical and versatile choice for processes requiring a non-reacting context. Understanding the abundance and application of noble gases emphasizes the significant role these elements play in daily life and technology.