This item tests selective methylation of morphine to yield different products depending on which site gets the methyl group. Codeine is the 3-O-methyl ether of morphine, formed by protecting or replacing the phenolic oxygen with a methyl group, leaving the nitrogen as a tertiary amine. If the methylating conditions are too strong or extensive, the methyl group can attach to the nitrogen too, producing a quaternary ammonium salt of morphine. That outcome is not codeine and reflects a different reaction path—N-methylation leading to a permanently charged species. So the statement about converting morphine to codeine but ending up with a quaternary salt in 1853 illustrates how reaction conditions can steer alkylation toward the nitrogen instead of the oxygen. This highlights the importance of selectivity in modifying alkaloids. The other proposed outcomes don’t capture this specific chemoselectivity issue.