( A ) In the highest oxidation states of the first five transition elements (Sc to Mn), all the 4s and 3d electrons are used for bonding
( B ) Once the $d^5$ configuration exceeded, the tendency to involve all the 3d electrons in bonding decreases.
( C ) In addition to the normal oxidation states, the zero oxidation state is also shown by these elements in complexes
( D ) In the highest oxidation states, the transition metal show basic character and form cationic complexes.
