Final answer:
Bethanechol is the drug that can be given orally to treat post-operative urinary retention.
Step-by-step explanation:
The drug that can be given orally to treat post-operative urinary retention is Bethanechol.
Bethanechol is a muscarinic agonist that stimulates the muscarinic acetylcholine receptors in the bladder, which leads to increased bladder contraction and improved urine flow.
Unlike atropine and scopolamine, which are muscarinic antagonists and would actually worsen urinary retention, bethanechol helps relieve the condition by enhancing bladder muscle activity.