Answer: The correct answer is Option b.
Explanation:
Reducing agents are defined as the agents which help the other substance to get reduced and itself gets oxidized. They undergo oxidation reaction.
[tex]X\rightarrow X^{n+}+ne^-[/tex]
For determination of reducing agents, we will look at the oxidation potentials of the substance. Oxidation potentials can be determined by reversing the standard reduction potentials.
For the given options:
This ion cannot be further oxidized because +1 is the most stable oxidation state of silver.
This metal can easily get oxidized to [tex]Pb^{2+}[/tex] ion and the standard oxidation potential for this is 0.13 V
[tex]Pb\rightarrow Pb^{2+}+2e^-;E^o_{(Pb/Pb^{2+})}=+0.13V[/tex]
This metal can easily get oxidized to [tex]H^{+}[/tex] ion and the standard oxidation potential for this is 0.0 V
[tex]H_2\rightarrow 2H^++2e^-;E^o_{(H_2/H^{+})}=0.0V[/tex]
This metal can easily get oxidized to [tex]Ag^{+}[/tex] ion and the standard oxidation potential for this is -0.80 V
[tex]Ag\rightarrow Ag^{+}+e^-;E^o_{(Ag/Ag^{+})}=-0.80V[/tex]
This ion cannot be further oxidized because +2 is the most stable oxidation state of magnesium.
By looking at the standard oxidation potential of the substances, the substance having highest positive [tex]E^o[/tex] potential will always get oxidized and will undergo oxidation reaction. Thus, considered as strong reducing agent.
From the above values, the correct answer is Option b.