I know the answers for these questions, I just want to learn why

1-
Use the table to determine which of the following species will convert Cd2+ to Cd.
A. Fe3+
B. Pb2+
C. Zn
D. Co2+
E. Sn

2-
Which of the following salts will form an acidic aqueous solution?
A. NaCl
B. NaCN
C. CaCl2
D. FeCl3
E. NaNO2

1 answer

Th first one is done with the activity series. Here is a link.
http://www.files.chem.vt.edu/RVGS/ACT/notes/activity_series.html
Here is the way it works. Any METAL in the activity series will displace any metal ION BELOW it in the series. Therefore, the answer must be a metal (only Zn and Sn qualify) and the answer must b a metal ABOVE Cd. Which one is that?

#2. Write the molecular hydrolysis equation for each.
I'll do one or two.
NaCl + HOH ==> NaOH + HCl.
Both NaOH and HCl are strong electrolytes so the salts are neutral.

NaCN + HOH ==> NaOH + HCN
NaOH is a strong base, HCN is a weak acid; therefore, the solution will be basic.

You can take it from here.