Final answer:
The instruction that should be given to the client is to continue medication use as prescribed.
Step-by-step explanation:
For a patient being discharged following in-patient treatment for pulmonary tuberculosis, it is important to give the instruction to continue medication use as prescribed (Option B). This is because tuberculosis is a chronic disease that requires long-term treatment, often lasting for months or years. Discontinuing medication before the prescribed course is complete can result in the reemergence of the infection and the development of drug-resistant strains of Mycobacterium tuberculosis. Therefore, it is crucial for the client to follow the prescribed medication regimen for the recommended duration to ensure successful treatment.