Calculate the number of unpaired electrons in the following gaseous ions: Mn3+, Cr3+, V3+, and Ti3+.

From the table given below: 

 Mn3+ : 3d4 unpaired electrons = 4

V3+ : 3d2 unpaired electrons =2

Cr3+ : 3d3 unpaired electrons= 3

Ti3+ : 3d1 unpaired electrons =1

Cr3+ is most stable in aqueous solution because of half filled d-orbital.