JEE Main 2021 · 16 March · morning · Single correct · +4 / −1
A group of 15 element, which is a metal and forms a hydride with strongest reducing power among group 15 hydrides. The element is :
- (a) As
- (b) Sb
- (c) Bi
- (d) P
Answer and solution
Answer (c) Bi
Solution
Chemistry ma’am · 3 steps
Go to the bottom of the group: that is where the true metal sits and where the E–H bond is weakest.
- Metallic character. Metallic character increases down group 15. N and P are non-metals, As and Sb are metalloids, and only Bi at the bottom is a true metal.
- Reducing power. Down the group the atom gets bigger, so the E–H bond gets longer and weaker. A weaker E–H bond breaks more easily and gives up hydrogen more readily, so reducing power increases from NH₃ to BiH₃.
Element Nature Hydride Reducing power P non-metal PH₃ weak As metalloid AsH₃ stronger Sb metalloid SbH₃ stronger still Bi metal BiH₃ strongest - So. Bi meets both conditions: it is the only true metal, and BiH₃ is the strongest reducing hydride of group 15. The answer is (c).
The idea to keep. Down group 15, the E–H bond weakens, so hydride stability falls and reducing power rises. Basicity of the hydrides falls in the same order, with NH₃ the most basic.
Answer from the NTA final answer key. Solution by PrepWiser.