Final answer:
The client with acute leukemia and mucositis should use a saline solution for oral care after meals and every 4 hours to avoid further irritation and promote healing.
Step-by-step explanation:
The nurse should advise the client with acute leukemia and mucositis that after every meal and every 4 hours while awake, they should use a saline solution for oral care. Mucositis can create a painful environment in the mouth, making it susceptible to infection. A mild, non-irritating saline solution can help in cleansing and keeping the mouth moist without causing further irritation, unlike lemon-glycerin swabs which can be harsh and desiccate oral tissues, commercial mouthwash which may contain alcohol or other irritants, or commercial toothpaste which might be abrasive. The goal is to maintain oral hygiene while minimizing the potential for further injury to the mucous membranes.