In the complex [Co(NH3)6]3+, there are six ammonia (NH3) ligands coordinated to the cobalt ion, giving it a coordination number of 6.

The complex [Co(en)2Cl2]+ can exhibit optical isomerism due to the presence of bidentate ligands (en = ethylenediamine) which can create non-superimposable mirror images.

The complex [Cr(en)3]3+ shows optical isomerism because it contains bidentate ligands (en = ethylenediamine) that can create non-superimposable mirror images.

[Ag(NH3)2]+ is a linear complex because silver (Ag) has a coordination number of 2 with two bidentate ligands.

The complex [Cr(NH3)6]3+ is octahedral with a coordination number of 6, as it is surrounded by six ammonia ligands.