Give reasons when Cl2 reacts with excess of F2, ClF3 is formed and not FCl3.

Fluorine shows an oxidation state of -1 only because it has no d orbital. In ClF3, the oxidation state of F is -1 and that of Cl is +3. This is possible. Also, in ClF3, the bigger Cl atom can easily accommodate 3 small sized F atoms, but in FCl3, the small sized F atom cannot easily accommodate 3 large sized Cl atoms.