Chemical Bonding And Molecular Structure

To arrange the hydrides in increasing order of thermal stability, we need to consider the strength of the hydrogen bonds in each compound. Generally, stronger hydrogen bonds lead to higher thermal stability.

The strength of hydrogen bonds generally follows the trend:

< < < <

Therefore, the correct answer is: A < E < B < D < C

P₄O₁₀ is a molecular compound with a specific arrangement of atoms that can be analyzed to determine the number of sigma (σ) bonds present. The structure comprises four phosphorus (P) atoms and ten oxygen (O) atoms. In the P₄O₁₀ molecule, the central P₄ forms a tetrahedral structure where each phosphorus atom is bonded to three others, creating six P-P single bonds. Each phosphorus is further bonded to four oxygen atoms, connecting through single bonds. Therefore, the bonds can be counted as follows:

1. P-P bonds: There are six P-P single bonds formed among the four phosphorus atoms.

2. P-O bonds: Each phosphorus atom forms four P-O single bonds, resulting in 4 × 4 = 16 P-O single bonds.

Adding these bonds together, the total number of σ bonds is calculated:
Total σ bonds = 6 (P-P) + 16 (P-O) = 22.

Hence, each pair of atoms forms a σ bond in covalent bondings, and the double bond between P and O has one σ bond. Therefore, the correct option counting only P-O single bonds without considering any double bonds is 16.

The given question requires us to arrange the substances based on the number of molecules present in 16 grams of each. To do this, we must calculate the number of moles in 16 g of each substance, as the number of molecules is proportional to the number of moles. The number of moles can be calculated using the formula:

moles = mass / molar mass

• O₂: The molar mass is 32 g/mol. The moles in 16 g = 16 g / 32 g/mol = 0.5 moles.
• CO₂: The molar mass is 44 g/mol. The moles in 16 g = 16 g / 44 g/mol ≈ 0.364 moles.
• CO: The molar mass is 28 g/mol. The moles in 16 g = 16 g / 28 g/mol ≈ 0.571 moles.
• H₂: The molar mass is 2 g/mol. The moles in 16 g = 16 g / 2 g/mol = 8 moles.

Now, we rearrange these based on the number of moles:

1. H₂: 8 moles
2. CO: ≈ 0.571 moles
3. O₂: 0.5 moles
4. CO₂: ≈ 0.364 moles

Thus, the order in decreasing number of molecules is (D), (C), (A), (B).