Highest oxidation state exhibited by a 3d-metal is

$(a)\;+2\qquad(b)\;+3\qquad(c)\;+7\qquad(d)\;+8$

Answer: The highest oxidation state exhibited by a 3d-metal is +7.
The maximum oxidation state is the sum of ns electrons and unpaired (n–1)d electrons.
This is highest for Mn where oxidation states from +2 to +7 are possible.
Note: The oxidation state increases with increase in atomic number & reaches a maximum in the middle and then decreases
edited Aug 4, 2014