Which one of the following hydride  is thermally most stable

Down the group as the size of the atom increases affinity of hydrogen towards central atom decreases. Thereforea) X-H bond enthalpy decreasesb) Thermal stability decreasesc) Reducing power increasesd) acidic strength (Ka) increasese) pKa decreasesDown the group as vanderwaal's forces increasesMelting and boiling points increasesExpected BP and MP….HF