copper react with sulfur to produce copper (1) sulfide according to the following equation
2Cu + S ----> CU2S
from the equation above 2 moles of copper react with 1 mole of Sulfur to produce 1 mole of copper (1) sulfide
therefore the mole ratio of Cu to CU2S is 2:1 therefore the moles of copper is 0.25 x 2= 0.5 moles
