Answer: [tex]NiO+CO\rightarrow Ni+CO_2[/tex]: reducing agent is CO.
Explanation:
a) [tex]Fe+Cu^{2+}\rightarrow Fe^{2+}+Cu[/tex]
The oxidation state of copper reduces from +2 to 0, it is getting reduced. As [tex]Cu^{2+}[/tex] gets reduced, it acts as an oxidising agent.
The oxidation state of iron increases from 0 to +2. Thus, it is getting oxidized. As [tex]Fe[/tex] gets oxidized, it acts as a reducing agent.
b. [tex]2Na+Cl_2\rightarrow 2NaCl[/tex]
The oxidation state of chlorine reduces from 0 to -1, it is getting reduced. As [tex]Cl_2[/tex] gets reduced, it acts as an oxidising agent.
The oxidation state of sodium increases from 0 to +1. Thus, it is getting oxidized. As [tex]Na[/tex] gets oxidized, it acts as a reducing agent.
c. [tex]C+O_2\rightarrow CO_2[/tex]
The oxidation state of oxygen reduces from 0 to -2, it is getting reduced. As [tex]O_2[/tex] gets reduced, it acts as an oxidising agent.
The oxidation state of carbon increases from 0 to +2. Thus, it is getting oxidized. As [tex]C[/tex] gets oxidized, it acts as a reducing agent.
d. [tex]NiO+CO\rightarrow Ni+CO_2[/tex]
The oxidation state of nickel reduces from +2 to 0, it is getting reduced. As [tex]Ni^{2+}[/tex] gets reduced, it acts as an oxidising agent.
The oxidation state of carbon increases from +2 to +4. Thus, it is getting oxidized. As [tex]CO[/tex] gets oxidized, it acts as a reducing agent.