Assign reason for each of the following :
(i) Transition elements exhibit paramagnetic behaviour .
(ii) `Co^(2+)` is easily oxidised in the presence of a strong ligand

Explanation

(i) The low ionisation potentials mean that the elements show variable valency states that compounds of the transtion element can be paramnetic .This suggests that the electrons which enter the d orbitals are being used
(ii) In presence of strong ligand the pairing of d electrons takes place and the valence shell electorinic configuration of `Co^(2)` and `CO^(3+)` ions can be represented as follow

Since the `l_(g)` level is at higher energy than `t_(2g)` level `Co^(2+)` ion is less stable than `Co^(3+)` ion morevoer the electrons in `l_(g)` level lower crystal field stablistion energy of `Co^(2+)` ion So `Co^(2+)` is easily oxidized to `CO^(3+)` in presence of a strong ligand