Question

Which of the following will not displace hydrogen?
A.Ba
B.Pb
C.Hg
D.Sn

Answer 1

Since, we know that the elements (other than hydrogen) that display a greater tendency to lose electrons to their solution are usually categorized as electropositive and the elements that acquire electrons are said to be electronegative. These elements usually lie below the element hydrogen in the series. And when we look at the electrochemical series, we can see that the order in which metals will replace one another from their salts. So, electropositive metals generally replace hydrogen from acids.

Complete answer:
The standard reduction potential of Ba, Pb, Hg, Sn and ${H_2}$ is -2.90, -0.126, 0.79, -0.136 and 0.0 (in V) respectively.
Elements having a more negative value of Standard reduction potential than hydrogen can displace hydrogen. Hence, Ba, Pb, and Sn will displace hydrogen.
Elements having a more positive value of SRP than hydrogen cannot displace hydrogen. Hence, Hg will not displace hydrogen.
Also, according to standard electrode, Ba, Pb and Sn have the lower reduction potential than H+ so, they can reduce it to ${H_2}$​ but as Hg has higher reduction potential than ${H^ + }$ so, it cannot reduce it.

Therefore, the correct answer is option (C).

Note:
The electrochemical series helps us to identify a good oxidizing agent or reducing agent. All the substances appearing on the top of the electrochemical series are a good oxidizing agent meaning they have positive Value of standard reduction potential whereas those appearing on the bottom of the electrochemical series are a good reducing agent meaning they have a negative value of standard reduction potential.