The correct answer is option 3: hypotonic solution. To understand why, let`s first understand what happens when a cell is placed in a hypotonic solution.

A hypotonic solution refers to a solution that has a lower concentration of solutes (particles) compared to the concentration inside the cell. When a cell is placed in a hypotonic solution, water molecules outside the cell move into the cell through osmosis. This influx of water into the cell causes the cell to swell up or expand, as the water moves from an area of lower concentration (outside the cell) to an area of higher concentration (inside the cell).

Now, let`s briefly see why the other options are incorrect:

1) Hypertonic solution: A hypertonic solution has a higher concentration of solutes compared to the cell. When a cell is placed in a hypertonic solution, water molecules move out of the cell, causing it to shrink or shrivel. This is the opposite of what happens when a cell swells up.

2) Isotonic solution: An isotonic solution has the same concentration of solutes as the cell. When a cell is placed in an isotonic solution, there is no net movement of water molecules. Therefore, the cell remains