Final answer:
The solution with Sn2+ ions will deposit reduced metal mass onto the cathode the fastest.
Step-by-step explanation:
The metal ion solution that will deposit reduced metal mass onto the cathode the fastest under identical current and concentration conditions is the solution of Sn2+ (tin ions).
According to the given information, the reduction reaction occurs at the cathode, which is the positive electrode. The reduction of Sn2+ ions to tin metal will result in the fastest deposition of reduced metal mass onto the cathode.
The other metal ion solutions (Ni2+, Pb2+, Cd2+, Ba2+) will also undergo reduction reactions at the cathode, but the rate of deposition may be slower compared to Sn2+.