**Core Concept**
The solubility of an inhalational anesthetic agent in blood is a key determinant of its onset and recovery times. Agents with higher blood solubility have slower onset and recovery. The **blood/gas partition coefficient** is a measure of this solubility.

**Why the Correct Answer is Right**
The correct answer is related to the agent's **blood/gas partition coefficient**, which is a measure of how the anesthetic distributes between blood and alveolar gas. A higher coefficient indicates higher solubility in blood, leading to slower equilibration between alveolar gas and arterial blood.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it has a lower blood/gas partition coefficient.
**Option B:** Incorrect as its solubility is not the highest among the options.
**Option C:** Incorrect due to its lower solubility compared to the correct answer.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that agents with high blood solubility, like the correct answer, have slower onset and recovery times due to the time it takes for the agent to equilibrate between blood and tissues.

**Correct Answer:** D. Diethyl ether is the most soluble in blood.