A,B,X,D and E are 15^th group elements. The correct trend of bond enthalpy is A-H > B-H > X-H > D-H > E-H. The element ‘X’ in the sequence is

detailed solution

Correct option is A

Down the group as the size of the atom increases affinity of hydrogen towards central atom decreases. Thereforea) X-H bond enthalpy decreases….N-H>P-H>As-H>Sb-H>Bi-H ;b) Thermal stability decreases….NH3>PH3>AsH3>SbH3>BiH3 ;NH3 is exothermic product,remaining four hydrides are endothermic products.c) Reducing power increases….NH3PH3>AsH3>SbH3>BiH3 ;Down the group as vanderwaal's forces increasesMelting and boiling points increasesExpected BP and MP….NH3PH3>AsH3>SbH3>BiH3 ;Down the group as the size of central atom increases, electron density on central atom decreases. Thusa) Basicity decreases,Lewis base strength decreases…..NH3>PH3>AsH3>SbH3>BiH3 ;b) Electron donating power decreases……NH3>PH3>AsH3>SbH3>BiH3 ;c) Ligand strength and ability to form dative bond decreases….NH3>PH3>AsH3>SbH3>BiH3 ;