**Core Concept**
Infusion of hypotonic saline can lead to changes in the distribution of fluids between the intracellular fluid (ICF) and the extracellular fluid (ECF) compartments in the body. This is due to the movement of water from areas of high concentration to areas of low concentration, as governed by the laws of osmosis.

**Why the Correct Answer is Right**
When hypotonic saline is infused, it dilutes the ECF, creating an osmotic gradient that favors the movement of water from the ICF to the ECF. As a result, both the ICF and ECF volumes increase. This is because the hypotonic saline solution has a lower concentration of solutes compared to the ECF, causing water to move out of the cells and into the ECF. This process is facilitated by the presence of aquaporin water channels in the cell membrane, which allow for the rapid movement of water molecules.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased ICF only - This option is incorrect because infusion of hypotonic saline would not cause an increase in ICF volume, as water would be moving out of the cells into the ECF.

**Option B:** Increased ECF only - This option is incorrect because while the ECF volume may increase initially, the ICF volume also increases due to the movement of water into the cells, driven by the osmotic gradient.

**Option D:** Increased ICF and decreased ECF - This option is incorrect because infusion of hypotonic saline would not cause a decrease in ECF volume; rather, it would lead to an increase in both ECF and ICF volumes.

**Clinical Pearl / High-Yield Fact**
When administering hypotonic saline, it is essential to monitor for signs of overhydration, such as pulmonary edema and cerebral edema, as the rapid movement of water into the ECF can lead to an increase in hydrostatic pressure and potentially life-threatening complications.

**✓ Correct Answer: C. Increased in both ICF and ECF**