Which one of the following has largest number of isomers? (R = alkyl group, en = ethylenediamine)

[Co (en)₂ Cl₂]+ has the largest number of isomers among the following. This includes the geometrical isomers i.e. cis and trans isomers and the stereoisomers which includes the d form, l form and the optically inactive molecules. [Ru(NH₃)₄ Cl₂]+ has two geometrical isomers cis and trans. [Co(NH₃)₅Cl]2+ has no isomers. [Ir(PR3)₂H(CO)]2+ has two geometrical isomers cis and trans. Hence, the correct answer is option (d).