Correct decreasing order of Thermal stability in 15th group hydrides is

All the hydrides of 15th  , 16th & 17thgroup are covalentIn 15th  , 16th & 17thgroup hydrides Down the group,As the size of the atom increases ,Affinity with Hydrogen decreases. Due to which(X=the central atom)A) X-H bond enthalpy decreasesB)Thermal stability decreasesC) X-H bond length increasesD) Acidic strength increasesE) Reducing power increases