Final answer:
A nurse should report a weight gain of 2 pounds in a client with heart failure as it may indicate fluid retention.
Step-by-step explanation:
A nurse caring for a client after hospitalization for heart failure should be attentive to any indicators of worsening condition. Among the options provided, the weight gain of 2 pounds should be reported to the provider. This weight gain could be a sign of fluid retention, which is a common and potentially serious issue for heart failure patients. In contrast, a blood pressure of 130/80 mm Hg is within a relatively normal range for someone with heart failure, decreased fatigue and shortness of breath indicates an improvement, and a serum potassium level of 3.5 mEq/L is a normal value.