Describe giving reason which one of the following pairs has the property indicated?
(a). `Fe` or `Cu` has higher melting point.
(b). `Co^(2+)` or `Ni^(2+)` has lower magnetic moment.

Explanation

(a). Fe has higher melting point than Cu. This is because Fe has four unpaired electrons in 3d-subshell while Cu has only one electron electron in the 4s-soubshell. Hence, metallic bonds in Fe are much stronger than those in Cu.
(b). `Co(Z=27)implies3d^74s^2,Ni^(2+)=3d^8` (2 unpaired electron). Hence, Ni has lower magnetic moment than Co,