(i) As electronegativity of halogens decreases in the order `F gt Cl gt Br`, the ionic character of transition metal halides decreases in the order `M - F gt M -Cl gt M-Br` . Hence, fluorides are ionic whereas chlorides and bromides are covalent.
(ii) The change in the size of the lanthanoids due in langthanoid contraction is very small as we proceed from`L a( Z =57)` to `Lu ( Z= 71)` . Hence, their chemical properties are similar. Moreover, their valence shell configuration remains the same because the electrons are added into the inner 4 f-subshell. Hence, they show similar chemical properties.
