Answer:
a). Coordination no. of
= 6
b). Coordination no. of
= 6
Explanation:
Coordination number is defined as number of donar atoms bonded to the central atom of the complex ion.
a). Coordination no. of
= 6
en or ethylenediamine is a bidentate ligand.
In bidentate ligand, two atoms directly bonded to the central atom.
NH3 is a unidentate ligand.
So, coordination no.= No. of bidentate ligand x 2 + No. of unidentate ligand
= 
b). Coordination no. of
= 6
Ethylenediamine (en) is a bidentate ligand.
oxalate ion (ox) is also a bidentate ligand.
Cl is a unidentate ligand
So, coordination no.= No. of bidentate ligand x 2 + No. of unidentate ligand
= 
Number one victory royal yaaa
C. The number of Valence electrons,
Every atom tries to follow the Octet rule i.e To have 8 electrons in its Valence shell.
Every atom tries to accomodate 8 electrons in its Valence shell to stabilize themselves, Metals usually have 1-3 eletrons in their Valence shell which they donate to non metals so their Valnce shell has 8 electroons, (The previous will now be the Valence shell and it will be full)
Similarly Non metals have 4-7 electrons, they accept electrons from metals so they can have 8 electrons in their Valence shell.
Noble gases already have 8 electrons in their Valance shell, so they do not react and stable.
Hope it helps :)