Final answer:
Methoxyflurane is the least soluble inhaled anesthetic compared to the widely used alternatives like desflurane, isoflurane, and sevoflurane, which have largely replaced the older and less safe diethyl ether.
Step-by-step explanation:
The least soluble inhaled anesthetic based on current medical use and literature is methoxyflurane. Today, the most widely used volatile anesthetics are desflurane, isoflurane, and sevoflurane, which are less flammable and safer in terms of the therapeutic index than the older, highly flammable compound diethyl ether.
However, while diethyl ether has a wide gap between the effective dose and the lethal dose, it is no longer the preferred anesthetic due to its flammability and side effects such as nausea. On the other hand, methoxyflurane, one of the older anesthetics, is known for its high solubility and slow onset and offset of action, making it less commonly used in practice due to longer recovery times.