If some blood cells are placed in a solution containing more than 0.9% (m/v) NaCl, then the water inside the cells will flow out of the cells and they will shrink. Such a solution is known as _____.

Hypertonic

The correct answer is Option (2) → Hypertonic

The movement of water across a semipermeable membrane due to concentration differences is called osmosis.

Blood cells normally remain stable in a 0.9% NaCl solution, which is known as an isotonic solution.

Case given in the question

The solution contains more than 0.9% NaCl.

This means:

• The solution outside the cell has higher solute concentration than inside the cell.
• Water moves out of the cell into the surrounding solution.
• As water leaves the cell, the cell shrinks.

This shrinking of red blood cells is called crenation.

A solution with higher solute concentration than the cell is called a hypertonic solution.

Option-wise Explanation

Option 1: Hypotonic

A hypotonic solution has lower solute concentration than the cell, causing water to enter the cell and the cell to swell. This is opposite to what is described. Hence this option is incorrect.

Option 2: Hypertonic

A hypertonic solution has higher solute concentration than the cell, causing water to move out of the cell and the cell to shrink. This matches the situation given in the question. Therefore this option is correct.

Option 3: Isotonic

An isotonic solution has the same solute concentration as the cell (about 0.9% NaCl), resulting in no net movement of water. Hence this option is incorrect.

Option 4: Hypsotonic

This term is not a correct biological classification for osmotic solutions. Therefore this option is incorrect.