Question

Which of the following is the weakest reducing agent?
(A) Atomic hydrogen
(B) Nascent hydrogen
(C) Molecular hydrogen
(D) Occluded hydrogen

Answer 1

Hint:As we know that hydrogen is the first element of the periodic table and the simplest in structure with one proton and one electron. Normally, hydrogen is found as hydrogen in nature and atomic hydrogen is formed by passing dihydrogen through an electric arc and nascent hydrogen is newly born hydrogen.

Complete answer:As we have already discussed that molecular hydrogen or ordinary hydrogen consists of diatomic molecules of two hydrogen atoms and due to its high hydrogen-hydrogen bond energy, this molecule is very stable and therefore does not react under ordinary conditions.
Next we have nascent hydrogen which as the name suggests it is a newly born hydrogen which is formed during the chemical reaction in aqueous solution. It is a powerful reducing agent as compared to molecular hydrogen.
Then we have atomic hydrogen which is formed by passing hydrogen gas through an electric arc struck between two tungsten filaments. Atomic hydrogen is very reactive and reduces oxides, chlorides, sulphides as well as sulphates of metals.
Lastly we have occluded hydrogen which is basically when molecular hydrogen is absorbed on a metal surface like iron, silver, platinum and palladium etc. this, so formed hydrogen is occluded.
So, in general the reactivity order of these hydrogen is as follows:
Molecular hydrogen < nascent hydrogen < atomic hydrogen.

Therefore, we can say that the correct answer is (C).

Note:Always remember that atomic hydrogen is a more powerful reducing agent than molecular hydrogen and nascent hydrogen. It is very unstable, having a very short half-life of a few seconds only. And nascent hydrogen is formed in situ whereas dihydrogen or molecular hydrogen is colourless and odourless and insoluble in water but it is highly combustible.