\(\left.\begin{array}{l} N \\ p \end{array}\right] \rightarrow\) Non metal

\(\left.\begin{array}{l} As \\ Sb \end{array}\right] \rightarrow\) Metalloid

\(Bi ] \rightarrow\) Metal

Hydrides of group \(15\) elements are \(NH _{3}\)

\(PH _{3}\)

\(AsH _{3}\)

\(SbH _{3}\)

\(BiH _{3}\)

In \(NH _{3}\), hydrogen atom gets partial positive charge due to less electronegativity.

But in \(BiH _{3},\) hydrogen atom gets partial negative charge because hydrogen is more electronegative than bismuth.

i.e. \(BiH _{3}\) is a strong reducing agent than others because we know that \(H\) is a strong reducing agent.