Give reason for the following features of transition metal chemistry:
(i). The lowest oxide of a transition metal (say, chromium, atomic number 24) is basic whereas the highest oxide is usually acidic.
(ii) . Transition metals sometimes exhibit very low oxidation states such as `+1` and 0.

Explanation

(i) Lowest oxide of Cr is CrO which is basic. The highest oxide is `CrO_(3)` which is acidic. ( In between `Cr_(2)O_(3)` is amphoteric ). Higher the oxidation state of the metal, more easily it can accept electron and hence greater is the acidic character.
(ii) ` + 1` oxidation state is shown by Cu because after loss of one electron, it acqires stable configuration of`3s^(10)`. Zero oxidation state is shown in forming metal carbonyls, e.g., `Ni(CO)_(4)` because`pi-` electrons donated by the ligands are accepted into the empty d orbitals.