Question

In the form of dichromate, \[\ce{Cr (VI)}\] is a strong oxidising agent in acidic medium but \[\ce{Mo (VI)}\] in \[\ce{MoO3}\] \[\ce{and W (VI)}\] in \[\ce{WO3}\] are not because:

(i) \[\ce{Cr(VI)}\] is more stable than \[\ce{Mo(VI)}\] and  \[\ce{and W(VI)}\].

(ii) \[\ce{Mo(VI)}\] and \[\ce{and W(VI)}\] are more stable than  \[\ce{Cr(VI)}\].

(iii) Higher oxidation states of heavier members of group-6 of transition series are more stable.

(iv) Lower oxidation states of heavier members of group-6 of transition series are more stable.

Answer 1

(ii) \[\ce{Mo(VI)}\] and \[\ce{and W(VI)}\] are more stable than  \[\ce{Cr(VI)}\].

(iii) Higher oxidation states of heavier members of group-6 of transition series are more stable.

Explanation:

In d-block elements, for heavier elements, the higher oxidation states are more stable. Hence, \[\ce{Mo(VI)}\] and \[\ce{W(VI)}\] are more stable than \[\ce{Cr(VI)}\]. That’s why, \[\ce{Cr(VI)}\] in the form of dichromate is a stronger oxidizing agent in acidic medium whereas \[\ce{MoO3}\] and \[\ce{WO3}\] are not.