Question

A group $15$ element, which is a metal and forms a $\mathrm{hydride}$ with the strongest reducing power among group $15$ $\mathrm{hydrides}$. The element is:

• A. $\mathrm{Bi}$
• B. $\mathrm{As}$
• C. $\mathrm{P}$
• D. $\mathrm{Sb}$

Answer 1

The correct option is A

$\mathrm{Bi}$

Group $15$ elements:

1. Elements in group $15$ are known as the elements of $\mathrm{nitrogen}$ family.
2. These elements have smaller sizes and greater nuclear charge.
3. Therefore they have higher electronegativity.
4. Also, the electronegativity of group $15$ elements decreases down the group.
5. Electronegativity is the tendency of an atom to attract electrons towards itself.
6. $\mathrm{Hydrides}$ of group $15$ elements are: ${\mathrm{NH}}_3$, ${\mathrm{PH}}_3$ ,${\mathrm{AsH}}_3$, ${\mathrm{SbH}}_3$ and ${\mathrm{BiH}}_3$
7. In ${\mathrm{NH}}_3$, $\mathrm{H}$ atom gets a partial positive charge due to low electronegativity.
8. In ${\mathrm{AsH}}_3,{\mathrm{PH}}_3\mathrm{and}{\mathrm{SbH}}_3$ $\mathrm{H}$ atom gets a partial negative charge but less negative in comparison to ${\mathrm{BiH}}_3$.
9. In ${\mathrm{BiH}}_3$, the hydrogen atom gets a high partial negative charge because hydrogen $\left(\mathrm{H}\right)$ is more electronegative than bismuth$\left(\mathrm{Bi}\right)$.
10. Hence, ${\mathbf{BiH}}_{\mathbf{3}}$ is a strong reducing agent than other elements of group $15$ because ${\mathrm{H}}^{-}$ is a strong reducing agent.
11. So, option A is correct.