D-block elements show great variety of oxidation states. Following are few statements related to this, identify the incorrect statement.
a. Mo⁺⁶ is more stable than Cr⁺⁶
b. Cr⁺² and Mn⁺³ show similar colour in aqueous solution, as they have same number of unpaired electrons
c. Iron can show +6 oxidation state
d. Cr₂O₇²⁻ is good oxidising agent in acidic medium