If a cell with 0.9% internal solute concentration is placed in a solution of 2.5% solute concentration. the 2.5% solution is said to be to the 0.9% cellular solute concentration.

Hypertonic

Explanation:

Tonicity refers to the concentration of solutes in a solution. Tonicity is the phenomenon that facilitates osmosis by forming a concentration gradient i.e. direction of flow of water in or out of the cell. The tonicity of a solution can either be hypertonic, hypotonic or isotonic. An hypertonic solution is that which contains high concentration of solutes in comparison to the intracellular solution. An hypotonic solution is that which contains low concentration of solutes in relation to the intracellular solution. A solution is said to be isotonic if it contains an equal amount of solute concentration with the intracellular solution.

According to the question, a cell contains 0.9% internal solute concentration while the extracellular solution contains 2.5% solute concentration. The solute concentration of the extracellular solution (2.5%) is higher than that of the cell (0.9%), hence, the extracellular solution is said to be HYPERTONIC to the cell's solution.

Based on the principle of OSMOSIS, which is the movement of water from a region of lower solute concentration to a region of high solute concentration via a semi-permeable membrane, water will ultimately move out of the cell due to the concentration gradient formed by the difference in solute concentration of both solutions.