Explain the following:
(a) Actinoids show large number of oxidation states.
(b) The transition metals form a large number of complex compounds.
(c) Chromium is a typical hard metal while mercury is a liquid.
(d) MnO is basic while `Mn_(2)O_(7)` is acidic in nature.
(e) Silver is a transition metal but zinc is not.

Explanation

(a) Due to comparable energies of 5f, 6 and 7s orbitals, all the electrons present in these subshells may participate in the bonding process, resulting in large number of oxidation states for actinoids.
(b) Transition metals form a large number of complexes because of small size and high charge of ions. They also have empty d-orbitals to accept the electron pairs from the ligands.
(c) Metal-metal interactions (metallic bonding) are strong in chromium due to the presence of six unpaired electrons in the 3d and 4s subshells.
In the case of mercury, all the electrons in the 5d and 6s subshells are paired and, therefore, the metal-metal interactions (or metallic bonding) are weak. That is why chromium is a typical hard metal but mercury is a liquid.
(d) Oxidation state of Mn in MnO is +2 while that in `Mn_(2)O_(7)` is +7. As the oxidation number of a metal increases, its acidic character increases due to decrease in the size of the metal ion and increase in charge density.
(e) Silver can exhibit +2 oxidation state in which it will have unpaired electrons in the d-orbitals. Thus, Ag is a transition metal. Zn does not form any ion with incomplete d-orbitals. The outer configuration of Ag and Zn metals are given below :
`Ag=[Kr]4d^(10)5s^(1)`
`Zn=[Ar]3d^(10)4s^(2)`