**Core Concept**
The question is testing the student's understanding of the pharmacological properties of anticholinesterases, specifically the distinction between tertiary amines and quaternary ammonium compounds. Anticholinesterases are a class of drugs that inhibit the enzyme acetylcholinesterase, thereby increasing the concentration of acetylcholine in the synaptic cleft.

**Why the Correct Answer is Right**
Tertiary amines, like drug 'X', are lipophilic and can cross the blood-brain barrier, making them more effective for treating central nervous system (CNS) disorders. On the other hand, quaternary ammonium compounds, like drug 'Y', are hydrophilic and cannot cross the blood-brain barrier, making them more effective for treating peripheral cholinergic disorders. This distinction is crucial in selecting the appropriate anticholinesterase for a particular condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide any relevant information to distinguish between drug 'X' and drug 'Y'. The statement is vague and does not address the pharmacological properties of the two drugs.
**Option B:** This option is incorrect because it is a distractor that tries to confuse the student with irrelevant information. The statement does not relate to the pharmacological properties of anticholinesterases.
**Option C:** This option is incorrect because it is a distractor that tries to confuse the student with a different class of drugs. The statement does not relate to the pharmacological properties of anticholinesterases.

**Clinical Pearl / High-Yield Fact**
When choosing an anticholinesterase, consider the location of the cholinergic disorder (CNS vs. peripheral) and the desired mechanism of action (central vs. peripheral). Tertiary amines are preferred for CNS disorders, while quaternary ammonium compounds are preferred for peripheral disorders.

**Correct Answer:** D.