In the form of dichromate, Cr (VI) is a strong oxidising agent in acidic medium but Mo (VI) in MoO3 and W (VI) in WO3 are not because ___________.

Higher oxidation states of heavier members of group 6 of transition series are more stable. So, Mo(VI) and W(VI) are more stable than Cr(VI). Because they are more stable, they will not get reduced(or act as oxidising agent). Cr(VI) on the other hand is not that stable and can easily get reduced to a lower oxidation state.

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