A student places four identical cells into four different liquids.

To determine which cell will look the smallest over time, we need to consider the process of osmosis and the relative salt concentrations of the cells and their surrounding liquids.

1. Cell W (Saltier than the cell): Since the liquid is saltier, water will move out of the cell into the liquid to try to balance the salt concentration. This will cause the cell to shrink.

2. Cell X (Less salty than the cell): Water will move into the cell (from the less salty liquid) as the concentration of salts outside the cell is lower than inside, making the cell swell.

3. Cell Y (Equally as salty as the cell): There will be no net movement of water in or out of the cell, so its size will remain the same.

4. Cell Z (Pure water with no salts): Since the liquid is pure water and lacks salts, water will move into the cell to balance the concentration, causing the cell to swell.

Based on this analysis, cell W, which is in the saltier liquid, will lose water and shrink the most. Therefore, over time, cell W will look the smallest.