Homoleptic complex from the following complexes is:

Complexes in which a metal is bound to only one kind of donor groups (ligands) are known as homoleptic complexes.

• In Potassium trioxalatoaluminate(III), $K_3[Al(C_2O_4)_3]$, the central metal ion Al(III) is bound to only one type of ligand, i.e., oxalato ($C_2O_4^{2-}$). Therefore, it is a homoleptic complex.
• In Triamminetriaquachromium(III), the central metal is bound to two types of ligands: ammine ($NH_3$) and aqua ($H_2O$). So, it is heteroleptic.
• In Diamminechloridonitrito-N-platinum(II), the central metal is bound to three types of ligands: ammine, chlorido, and nitrito-N. So, it is heteroleptic.
• In Pentaamminecarbonatocobalt(III) chloride, the central metal is bound to two types of ligands: ammine and carbonato. So, it is heteroleptic.