Question

Given below are two statements :
Statement I : The correct order in terms of bond dissociation enthalpy is \( Cl_2>Br_2>F_2>I_2 \).
Statement II : The correct trend in the covalent character of the metal halides is \( SnCl_2>SnCl_4 \), \( PbCl_2>PbCl_4 \) and \( UF_4>UF_6 \).
In the light of the above statements, choose the correct answer from the options given below :

• A. Both Statement I and Statement II are true
• B. Statement I is false but Statement II is true
• C. Statement I is true but Statement II is false
• D. Both Statement I and Statement II are false

Hint:

Fluorine's anomalous low bond enthalpy is a classic exam question—always attribute it to inter-electronic repulsion of lone pairs due to its tiny size.

Answer 1

The Correct Option is C

Let's analyze each statement to determine their correctness:

Statement I: The statement claims that the correct order of bond dissociation enthalpy is \( Cl_2>Br_2>F_2>I_2 \).

• Bond dissociation enthalpy refers to the energy required to break the bonds between atoms in a molecule. Generally, it is expected to follow the trend where molecules with stronger bonds have higher enthalpy.
• Chlorine (\(Cl_2\)) has a stronger bond compared to Bromine (\(Br_2\)), which in turn is stronger than Fluorine (\(F_2\)) due to smaller atomic size causing stronger repulsion between lone pairs. Iodine (\(I_2\)) has the weakest bond due to its large atomic size leading to weaker overlap.
• Therefore, the order of bond dissociation enthalpy as mentioned in the statement is correct: \( Cl_2 > Br_2 > F_2 > I_2 \).

Statement II: The statement discusses the trend in the covalent character of the given metal halides.

• Generally, covalent character in metal halides can be influenced by the oxidation state of the metal and the nature of the halogen. As the oxidation state increases, covalent character increases as per Fajans' rule.
• The correct trend should be that a higher oxidation state leads to more covalent character: \( SnCl_4 \) is more covalent than \( SnCl_2 \), and similarly \( PbCl_4 \) is more covalent than \( PbCl_2 \).
• Thus, the given order \( SnCl_2 > SnCl_4 \) and \( PbCl_2 > PbCl_4 \) is incorrect. However, \( UF_4 \) is indeed less covalent than \( UF_6 \), which aligns with the same concept but does not make the overall statement true.

Conclusion: Based on the analysis:

• Statement I is true as the order is correct concerning bond dissociation enthalpy.
• Statement II is false as it incorrectly stipulates the trend in covalent character for \( SnCl_2 \), \( SnCl_4 \), \( PbCl_2 \), and \( PbCl_4 \).

Therefore, the correct answer is: Statement I is true but Statement II is false.