Answer
[tex][kr]4d^4[/tex]
Explanation
Given that the tc atom has electronic configuration [tex]tc=[kr]5s^24d^5[/tex] we find the electronic configuration of the ion as follows
Step 1
Because the 5s orbital is further away than the 4d from the nucleus , during the ionization process the two 5s electrons will be removed first. As as result the [tex]tc^{2+}[/tex] has electronic configuration [tex][kr]4d^5.[/tex]
Step 2
All that is left is to remove one more electron. This electron is removed from the 4d orbital. As a result, the [tex]tc^{3+}[/tex] ion has electronic configuration
[tex]tc^{3+}=[kr]4d^4.[/tex]
