How would you account for the following ?
(i) Many of the transition elements are known to form interstitial compound ?
(ii) The metallic radii of third (5d) series of transition metals are virtually the same as those of the corresponding group member of second (4d) series.
(iii) Lanthanoids form primarily +3 ions while the actinoids usually have higher oxidation state in their compounds, +4 or even +6 being typical.
