Which one of the following complexes shows optical isomerism? (en = ethylenediamine)

Question

Which one of the following complexes shows optical isomerism?
(en = ethylenediamine)

cis[Co(en)₂Cl₂]Cl

trans[Co(en)₂Cl₂]Cl

[Co(NH₃)₄Cl₂]Cl

[Co(NH₃)₃Cl₃]

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