(a) Complete the following equation :
(i) `CrO_(4)^(2-)+2OH^(-)rarr`
(ii) `MnO_(4)^(-)+4H^(+)+3e^(-)rarr`
(b) Account for the following :
(i)Zn is not considered as transition element
(ii) Transition metals form a large number of complexes
(iii) The `E^(@)` value for the `(Mn^(3+))/(Mn^(2+))` couple is much more positive than for `(Cr^(3+))/(Cr^(2+))`couple.

Explanation

(a)(i)`Cr_(2)O_(7)^(-2)+2OHrarr2crO_(4)^(-2)+H_(2)O`
(ii)`MnO_(4)+4H+3e^(-)rarrrMnO_(2)+2H_(2)O`
(b) (i) Because Zn has complelety filled d orbital
(ii) Smaller sizes of metal ion high ionic changes vacant d orbital
(iii) `Mn^(3+)` less stable than `Mn^(2+)`(3ds) which is stabel half filled configuration `Cr^(3+)` has stable `t_(22)g^(3)` configureation `Cr^(3+)` cannot reduce to `Cr^(2+)`
(i) with reference to structural variabliltiy and chemical reactivity write the differenence between lanthanoids and actinoids
(ii) Name a memeber of the lanthanoid series which is well known to exhibit + 4 oxidation state
(iii) Complelte the following equation : `MnO_(4)^(-)+8H^(+)+5e^(-)rarr`
(iv) out of `Mn^(+)` and `Cr^(3+)` which is more paramagnetic and why ? Atomic nos : Mn =25
Cr =24