In which of the fallowing molecule have fourth highest enthalpy of formation $$($$∆Hf $$)$$ of in $$15th$$ group $$hydrides($$ $$EH3)A=NH3$$, $$B=$$ $$PH3$$, $$C=AsH3$$, $$D=$$ $$SbH3$$ $$E=$$ $$BiH3$$

Question

In which of the fallowing molecule have fourth highest enthalpy of formation $$($$∆Hf $$)$$ of   in $$15th$$ group $$hydrides($$ $$EH3)A=NH3$$, $$B=$$ $$PH3$$, $$C=AsH3$$, $$D=$$ $$SbH3$$  $$E=$$ $$BiH3$$

Infinity Learn · Accepted Answer

All the elements of Group $$15$$ form hydrides of the type $$EH3$$ where E $$=$$ N, P, As, Sb or Bi. The hydrides show regular gradation in their properties. The stability of hydrides decreases from $$NH3$$ to $$BiH3$$ which can be observed from their bond dissociation enthalpy. Consequently, the reducing character of the hydrides increases. Ammonia is only a mild reducing agent while $$BiH3$$ is the strongest reducing agent amongst all the hydrides. Basicity also decreases in the order $$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3$$. Due to high electronegativity and small size of nitrogen, $$NH3$$ exhibits hydrogen bonding in solid as well as liquid state. Because of this, it has higher melting and boiling points than that of $$PH3$$ .Central atom size order :$$NH3$$ < $$PH3$$ < $$AsH3$$ < $$SbH3$$ < $$BiH3Bond$$ length order: $$NH3$$ < $$PH3$$ < $$AsH3$$ < $$SbH3$$ < $$BiH3Bond$$ energy order :$$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3Enthalpy$$ of formation order:$$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3Bond$$ angle order : $$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3Thermal$$ stability order : $$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3Basic$$ nature order :$$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3Reducing$$ power order :$$NH3$$ < $$PH3$$ < $$AsH3$$ < $$SbH3$$ < $$BiH3H-$$ bonding capacity order : $$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3Central$$ atom electro negativity order :$$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3S-character$$ percentage at central atom order : $$NH3$$ > $$PH3$$ > $$AsH3$$ > $$SbH3$$ > $$BiH3Melting$$ point order : $$PH3$$ < $$AsH3$$ < $$SbH3$$ < $$NH3$$< $$BiH3Boiling$$ point order : $$PH3$$ < $$AsH3$$ $$AsH3$$ > $$SbH3$$ > $$NH3$$ >$$BiH3Enthalpy$$ of vapourisation : $$PH3$$ < $$AsH3$$ < $$SbH3$$ < $$NH3$$< $$BiH3$$

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