Q.Assertion: bond dissociation energy of fluorine is greater than chlorine gas
Reason: chlorine has more electronic repulsion than fluorine

Step 1. Check the assertion against known bond dissociation enthalpies.

Experimentally, the F-F bond dissociation enthalpy (~159 kJ/mol) is actually LOWER than the Cl-Cl bond dissociation enthalpy (~242 kJ/mol) — chlorine's bond is the stronger of the two, the opposite of what the assertion claims. So the assertion is false.

Step 2. Check the reason.

The anomalously low F-F bond energy is explained by fluorine's very small atomic size, which forces the three non-bonding lone pairs on each fluorine atom unusually close together across the short F-F bond, causing significant lone-pair-lone-pair electronic repulsion that weakens the bond. Chlorine, being a larger atom, has a longer Cl-Cl bond and correspondingly much less lone-pair repulsion. So it is fluorine, not chlorine, that has the greater electronic repulsion — the reason as stated is also false. …

Independently verify the assertion and the reason against the real bond-dissociation-enthalpy data and the accepted explanation (fluorine's small size causing lone-pair repulsion), rat …

Assuming fluorine, being the most reactive and most electronegative halogen, must also have the strongest X-X bond — reactivity and bond strength are not the same …