The correct answer is option 2, which is water. The behavior of the liquid indicates that it undergoes a unique phase change known as the anomalous expansion of water.

When most liquids are cooled, they contract and reduce in volume. However, water behaves differently. Initially, as water is cooled down to 4°C, it contracts as expected. But when it is further cooled down to 0°C, it starts to expand instead of contracting.

This expansion can be attributed to the formation of hydrogen bonds between water molecules. At temperatures above 4°C, water molecules have enough thermal energy to overcome the attractive forces between them and move more freely, resulting in the contraction of the liquid.

As the temperature reaches 4°C, the water molecules start forming more hydrogen bonds, which increases the intermolecular forces and causes the expansion. This expansion continues until the water freezes into ice at 0°C.

It is important to note that this anomalous behavior of water is not exhibited by all liquids. Therefore, option 2, water, is the correct answer.