Textbook problem 2A.11

[505934309]

Hello,

I am working on textbook problem 2A.11 and can someone clarify why the answer for a. is not Fe2+? I am assuming this has to do with the M cation.

[Reva Patel 2F]

So, for this problem it indiciates the the given atom is in the form M3+, which means the metal has 3+ charge. If the electron config of the cation is [Ar]3d^6, that means that prior to the 3+ change, the metal's charge is [Ar]3d^74s^2, since after removing 3 electrons the configuration would be [Ar]3d^6. If we find the element that matches up with the configuration: [Ar]3d^74s^2, it is Co+3