You are attempting the reduction of quinone with sodium borohydride. After adding the 0.05 g of NaBH4 you note that the solution remains yellow. Following the procedure, you continue to add increments of 0.05 g NaBH4. You note that the yellow color remains even after the addition of 0.10 g of extra NaBH4. Several students around you are experiencing a similar problem. Propose a cause for this and suggest a solution.