Question

Which is a stronger reducing agent, $Sb{H_3}$or $Bi{H_3}$,and why?

Answer 1

Hint: A strong oxidising agent is one which gets reduced easily and a strong reducing agent is one which gets oxidised easily. This means the stronger reducing agent will be the one which can easily release the hydrogen and form the respective cations thereby getting oxidised.

Step-by-step explanation:
Step 1
The group $15$ of the periodic table consists of the following elements: nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and Bismuth (Bi). They belong to the p-block and are known as the representative elements.
Step 2
On moving down the group, the size of the atoms increases gradually because of the addition of an electron shell for the succeeding elements. As the size of the atom increases, the ionization energy decreases moving from nitrogen to bismuth.
Step 3
The members of Group 15 form hydrides of the type $M{H_3}$. The thermal stability of the hydrides of Group 15 elements decreases as we move down the group. $Bi{H_3}$is extremely unstable and is being found in traces. This is because as we move down the group, the $M - H$ bond energy decreases and consequently the thermal stability of the hydrides decreases on moving down the group. Thus, the reducing character of the hydrides also decreases on moving from $N{H_3}to Bi{H_3}$. It is due to the fact that as the thermal stability of the hydrides decreases down the group, so their tendency to give off hydrogen and act as a reducing agent increases from $N{H_3}to Bi{H_3}$.
Hence, $Bi{H_3}$ is a stronger reducing agent than $Sb{H_3}$.

Note: A strong reducing agent is a substance which itself undergoes oxidation in order to facilitate the process of reduction.Lithium, having the largest negative value of electrode potential, is the strongest reducing agent.