**Core Concept**
The body's response to insulin administration involves the regulation of glucose levels in the extracellular fluid (ECF) compartment. Insulin promotes glucose uptake in cells, thereby reducing the glucose concentration in the blood and ECF.

**Why the Correct Answer is Right**
Insulin binds to its receptor on the surface of cell membranes, triggering a signaling cascade that activates the enzyme glycogen synthase, leading to glycogen synthesis and glucose storage within cells. As a result, glucose is removed from the ECF, causing a decrease in blood glucose levels. This process is mediated by the insulin receptor substrate (IRS) proteins and the phosphatidylinositol 3-kinase (PI3K) pathway.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option would imply an increase in ECF glucose concentration, which contradicts the effects of insulin on glucose metabolism.
* **Option B:** This option is incorrect because insulin administration does not directly cause a decrease in ECF volume.
* **Option D:** This option is incorrect because insulin administration primarily affects glucose metabolism and does not directly alter the concentration of other electrolytes in the ECF.

**Clinical Pearl / High-Yield Fact**
Insulin resistance, a condition characterized by reduced insulin sensitivity, can lead to hyperglycemia and is a key feature of type 2 diabetes mellitus.

**Correct Answer: B. Decrease**