A group 15 element, which is a metal and forms a hydride with strongest reducing power among group 15 hydrides. The element is :
(1) P (2) Bi (3) Sb (4) As
Best answer
The correct answer is option 2 ) Bi
Answer: (2) Bi
Down group 15 the size of the atom increases, so the E–H bond in the hydrides \(\mathrm{NH_3, PH_3, AsH_3, SbH_3, BiH_3}\) becomes longer and weaker. A weaker bond means the hydride gives up hydrogen more easily, so reducing power increases: \(\mathrm{NH_3 < PH_3 < AsH_3 < SbH_3 < BiH_3}\).
Bismuth is the only true metal in the group (N and P are non-metals, As and Sb are metalloids), and \(\mathrm{BiH_3}\) is the strongest reducing agent, so the element is Bi.
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