The correct answer is option 2: Hypotonic solution.

When a cell is placed in a hypotonic solution, it means that the concentration of solutes (such as salt or sugar) outside the cell is lower than the concentration inside the cell. As a result, water molecules move into the cell through a process called osmosis, in an attempt to equalize the concentration on both sides of the cell membrane. This influx of water causes the cell to swell and increase in volume.

In contrast, when a cell is placed in a hypertonic solution (option 1), the concentration of solutes outside the cell is higher than inside the cell. This causes water molecules to move out of the cell, resulting in the cell shrinking and decreasing in volume.

Option 3, isotonic solution, refers to a solution where the concentration of solutes is equal on both sides of the cell membrane. In an isotonic solution, there is no net movement of water, so the cell volume remains constant.

Option 4, "none of these", is not the correct answer as the cell volume does indeed change when placed in a specific type of solution.