a)
- Oxidized: \(\mathrm{Cr}^{+}\)
 
- Reduced: \(\mathrm{Sn}^{4+}\)
 
- Reducing agent: \(\mathrm{Cr}^{+}\)
 
- Oxidizing agent: \(\mathrm{Sn}^{4+}\)
 
\(\boxed{\text{Oxidized: } \mathrm{Cr}^{+}, \text{ Reduced: } \mathrm{Sn}^{4+}, \text{ Reducing agent: } \mathrm{Cr}^{+}, \text{ Oxidizing agent: } \mathrm{Sn}^{4+}}\)
b)
- Oxidized: \(\mathrm{Fe}\)
 
- Reduced: \(\mathrm{Hg}^{2+}\)
 
- Reducing agent: \(\mathrm{Fe}\)
 
- Oxidizing agent: \(\mathrm{Hg}^{2+}\)
 
\(\boxed{\text{Oxidized: } \mathrm{Fe}, \text{ Reduced: } \mathrm{Hg}^{2+}, \text{ Reducing agent: } \mathrm{Fe}, \text{ Oxidizing agent: } \mathrm{Hg}^{2+}}\)
c)
- Oxidized: \(\mathrm{As}\)
 
- Reduced: \(\mathrm{Cl}_{2}\)
 
- Reducing agent: \(\mathrm{As}\)
 
- Oxidizing agent: \(\mathrm{Cl}_{2}\)
 
\(\boxed{\text{Oxidized: } \mathrm{As}, \text{ Reduced: } \mathrm{Cl}_{2}, \text{ Reducing agent: } \mathrm{As}, \text{ Oxidizing agent: } \mathrm{Cl}_{2}}\)