(a) What happens when
(i) Manganate ions `(MnO_(4)^(2-))` undergoes disproportionation reaction in acidic medium ?
(ii) Lanthanum is heated with Sulphur?
(b) Explain the following trends in the properties of the members of the First series of transition elements:
(i) ` E^(@) (M^(2+)//M)` value for copper is positive `(+ 0.34 V)` in contrast to the other members of the series.
(ii) `Cr^(2+)` is reducing while `Mn^(3+)` is oxidising, though both have `d^(4)` configuration.
(iii) The oxidising power in the series increases in the order `VO_(2)^(+) lt Cr_(2)O_(7)^(2-) lt MnO_94)^(-)`.

Explanation

Reduction potential will depend on
`Cu(s)toCu(g),triangleH(atomisation)`
`(ii)Cu(g)toCu^(2+),(IE_(1)+IE_(2))`
`(iii)Cu^(2+)overset(H_(2)O)toCu^(2+),(triangleH_(Hyd))`
Due to high enthalpy of atomisation and low `triangleH_(hydration)` energy `E^(@)_(cu^(+2)//Cu)`is high