Final answer:
The staff nurse likely caused the reaction by adding the medication to the diluent without allowing it to reach room temperature.
Step-by-step explanation:
The staff nurse likely caused the reaction by adding the medication to the diluent without allowing it to reach room temperature. When a medication is mixed with a diluent, it is important for both substances to be at the same temperature to prevent any chemical reactions or precipitates from occurring.
In this case, if the medication was added to the diluent without allowing it to reach room temperature, it could have caused a reaction that resulted in the appearance of precipitate in the syringe. To avoid this, the medication should be allowed to reach room temperature before being added to the diluent.