The three substances that can reduce Ag+ to Ag, but will not reduce Sn2+ to Sn are
Zn, Pb, H2, Mg, Cu, I2, Al, Ca
Zn, Pb, Mg, Al, Ca will reduce Ag^+ to Ag BUT they also will reduce Sn^2+. See this site.
http://www.csudh.edu/oliver/chemdata/data-e.htm
To determine which substances can reduce Ag+ to Ag but will not reduce Sn2+ to Sn, we need to refer to their respective reduction potentials. Reduction potential is a measure of the tendency for a substance to gain electrons and undergo reduction.
By comparing the reduction potentials of the substances, we can determine their relative ability to reduce Ag+ and Sn2+ ions. The more positive the reduction potential, the stronger the substance is as a reducing agent.
Here are the reduction potentials for the substances mentioned:
Zn: -0.76 V
Pb: -0.13 V
H2: 0.00 V
Mg: -2.37 V
Cu: +0.34 V
I2: +0.54 V
Al: -1.66 V
Ca: -2.76 V
From the list, we need to find substances that have reduction potentials more positive than that of Ag+ (+0.80 V). This indicates that they are capable of reducing Ag+ to Ag. However, we also need to ensure that these substances have reduction potentials less positive than that of Sn2+ (-0.14 V), as otherwise, they would also be able to reduce Sn2+ to Sn.
Based on this information, the substances that can reduce Ag+ to Ag but will not reduce Sn2+ to Sn are Zn and Pb. Their reduction potentials (+0.34 V and -0.13 V, respectively) are more positive than that of Ag+ and less positive than that of Sn2+.