Final answer:
The nurse should assess the older client with a nasogastric tube first.
Step-by-step explanation:
In this scenario, the nurse is caring for several clients at risk for overhydration. The nurse needs to assess the older client with different factors in mind. Out of the options provided, the most relevant finding to assess first would be B) Had abdominal surgery and has a nasogastric tube. This is because the nasogastric tube can contribute to excessive fluid intake and increase the risk of overhydration.