Final answer:
The best approach for the nurse to take when implementing relaxation techniques for a 12-year-old in sickle-cell crisis is to encourage the child to engage in deep breathing exercises.
Step-by-step explanation:
The best approach for the nurse to take when implementing relaxation techniques for a 12-year-old in sickle-cell crisis is Option 1: Encourage the child to engage in deep breathing exercises. Deep breathing exercises can help reduce tension and promote relaxation by slowing down the heart rate and decreasing muscle tension. It is a simple and effective technique that can be done anywhere, at any time.