Statement I: The bond dissociation enthalpy of halogens follows the order Cl2>Br2>F2>I2. The bond energy of F2 is lower than Cl2 and Br2 due to the high inter-electronic repulsion between the lone pairs on the small fluorine atoms. Thus, Statement I is true.
Statement II: According to Fajan's rules, for a given metal, the compound with the metal in a higher oxidation state has more covalent character due to higher polarizing power. Therefore, SnCl4>SnCl2 and PbCl4>PbCl2 are correct. However, for Uranium halides, UF6 has a higher oxidation state (+6) than UF4 (+4), so UF6 is more covalent than UF4. The statement claims UF4>UF6, which is incorrect. Thus, Statement II is false.