Final answer:
The [Cr(H₂O)₆]Cl₂ and [Fe(H₂O)₆]Cl₂ complexes are reducing in nature because of the presence of unpaired electrons in their d-orbitals.
Step-by-step explanation:
The assertion that [Cr(H₂O)₆]Cl₂ and [Fe(H₂O)₆]Cl₂ are reducing in nature is true. The reason that unpaired electrons are present in d-orbitals is also true. Therefore, the correct option is D. Assertion and reason both are true, reason is correct explanation of assertion.