Given below are two statements :
Statement : The correct order in terms of bond dissociation enthalpy is .
Statement : The correct trend in the covalent character of the metal halides is , and .
In the light of the above statements, choose the correct answer from the options given below :
Both Statement and Statement are true
Statement is false but Statement is true
Statement is true but Statement is false
Both Statement and Statement are false
Correct answer:C
Standard Method
Given: Two statements are given about bond dissociation enthalpy of halogens and covalent character of metal halides.
Find: Which option correctly identifies the truth values of Statement and Statement .
Bond dissociation enthalpy in halogens depends on bond length and lone pair-lone pair repulsion. Covalent character in metal halides is explained using Fajan's rules.
Statement I: In general, bond strength decreases down the group as atomic size increases. However, shows anomalously low bond enthalpy because the very small size of fluorine causes strong repulsion between lone pairs on adjacent atoms.
The experimental order is
So Statement is true.
Statement II: By Fajan's rules, a cation with higher charge and smaller size has greater polarizing power and forms a bond with more covalent character.
Therefore:
Hence the given trend is reversed, so Statement is false.
Therefore, Statement is true but Statement is false. The correct option is C.
Assuming bond dissociation enthalpy always decreases strictly upward or downward in the halogen group is incorrect because is anomalous. The lone pair-lone pair repulsion in fluorine weakens the bond. Always account for this exception before writing the order.
Applying Fajan's rules in the wrong direction is a common error. Higher charge and smaller cation size increase polarizing power, which increases covalent character. So makes more covalent than , not the reverse.
Comparing only oxidation state without relating it to ionic size and polarization can lead to confusion in pairs like and . Use the full Fajan's rules argument instead of memorizing isolated trends.
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