The correct option is
D 1.32According to the law of conservation of mass, “Mass can neither be created nor be destroyed but can be transformed from one form to another”. Which can be interpreted as, the mass of reactants= the mass of products.
Mass of Cu before reaction + mass of S before reaction = mass of CuS formed + unreactedS
Therefore mass of unreacted S=3.17 g+2.93 g−4.78 g=1.32 g