(a) Complete the following chemical reaction equations :
(i) `MnO_(4(aq))^(-) + C_(2)O_(4(aq))^(2-) + H_((aq))^(+) to `
(ii) `Cr_(2) O_(7 (aq))^(2-) + Fe_((aq))^(2+) + H_((aq))^(+) to `
(b) Explain the following observations about the transition/inner transition elements :
(i) There is in general an increase in density of element from titanium (Z = 22) to copper ( Z= 29).
(ii) There occurs much more frequent metal-metal bonding in compounds of heavy transition elements (`3^(rd)` series).
(iii) The members in the actinoid series exhibit a larger number of oxidation states than the corresponding members in the lanthanoid series.

Explanation

(i) `5 C_(2)O_(4)^(2-) + 2Mn O_(4)^(-) + 16 H^(+) to 2Mn^(2+) + 8H_(2)O + 10 CO_(2)`
(ii) `Cr_(2)O_(7)^(2-) + 6Fe^(2+) + 14 H^(+) to 2Cr^(3+) + 6 Fe^(3+) + 7H_(2)O`
(b) (i) As we move along a transition series from left to right (i.e. Ti to Cu) , the atomic radii decrease due to increase in nuclear charge . Hence the atomic volume decreases. At the same time , atomic mass increases. Hence the density from Titanium (Ti) to Copper (Cu) increases.
(ii) Since `3^(rd)` series of transition elements show the variable oxidation state .
(iii) Actinoids series show a large number of oxidation state due to very small energy gap between 5f , 6 d and 7s subsells.