That would be A.
2.5*2*10^(10-7)=5*10^3
I would say that B is the correct answer which means that the melting point would be intensive or that no matter how large or small the sample of the sulphur is, it will have a consistent melting temperature or of 115.2 degrees C.
The reaction between Na2S and CuSO4 will give us the balanced chemical reaction of,
Na2S + CUSO4 --> Na2SO4 + CuS
This means that for every 78g of Na2S, there needs to be 159.6 g of CuSO4. The ratio is equal to 0.4887 of Na2S: 1 of CuSO4. Thus, for every 12.1g of CuSO4, we need only 5.91 g of Na2S. Thus, there is an excess of 9.58 g of Na2S. The answer is letter C.
