A liquid initially contracts when cooled down to 4°C but on further cooling down to 0°C, it expands. The liquid is :

The liquid described is water, which exhibits a unique property known as the anomalous expansion of water. Most substances contract monotonically when cooled, but water behaves differently between 4°C and 0°C [1]. As water is cooled from room temperature, it initially contracts and its density increases until it reaches its maximum density at approximately 4°C. Upon further cooling from 4°C down to 0°C, water begins to expand, meaning its volume increases and its density decreases. This expansion continues as it freezes into ice, which is why ice floats on liquid water. This behavior is attributed to the specific hydrogen bonding network that forms a more open structure at lower temperatures. In contrast, substances like mercury, alcohol, and molten iron typically follow the standard rule of thermal contraction upon cooling.

Sources

1. [1] https://ncert.nic.in/textbook/pdf/keph203.pdf