Two elements in the second transition series ( through ) have four unpaired electrons in their 3+ ions. what elements fit this description? (enter multiple answers as a comma-separated list.)

Technetium and Rhodium in the second transition series have four unpaired electrons in their 3+ ions.

Explanation:

Electronic Configuration of Tc (Technetium) is

                                          [Kr] 4d⁵, 5s²

And 
Electronic Configuration of Tc³⁺ (Technetium) is,

                                          [Kr] 4d⁴

These 4 electrons exist unpaired in d-orbitals, i.e.
         
                                              ↑, ↑, ↑, ↑


And Electronic Configuration of Rh (Rhodium) is

                                          [Kr] 4d⁸, 5s¹

And 
Electronic Configuration of Rh³⁺ is,

                                          [Kr] 4d⁶

Among these 6 electrons, 2 electrons exist in pair while 4 exist unpaired in d-orbitals, i.e.
         
                                              ↑↓,  ↑, ↑, ↑, ↑