no of moles of Cu  = W/G.A.Wt
                          Â
= 1/63.546Â Â = 0.015736 moles
5Cu(s)Â Â + 9X-------------> Cu5X9
5 moles of Cu react with excess of X to gives 1 mole of
Cu5X9
0.015736moles of Cu react with excess of X to gives =
1*0.015736/5 = 0.0031472moles fo Cu5X9
molar mass of Cu5X9Â Â Â Â = mass of Cu5X9/no
of moles
                                  Â
= 1.908/0.0031472Â Â Â = 606.25g/mole
9 atoms molar mass of XÂ Â = molar mass of Cu5X9-
atomic mass of Cu
                         Â
= 606.25-5*63.546
                         Â
= 288.52
atomic mass of XÂ Â = 288.52/9Â Â =
32.06g/mole
The unknown element X is sulfur
sulfur >>>>answer
