Answer: Water is the only substance that is lighter as a solid than as a liquid. Thus, it is unique in its physical properties.
Step-by-step explanation:
A property that does not bring any change in chemical composition of a substance are known as physical properties.
For example, shape, size, mass, volume, density, etc of a substance are all physical properties.
On the other hand, a property that changes chemical composition of a substance is known as chemical property.
For example, precipitation, reactivity, toxicity etc are chemical property.
In solid state, water has cage like structure due to which there is space present within its molecules. As a result, it becomes lighter in nature.
Hence, water is the only substance that is lighter as a solid than as a liquid. Thus, it is unique in its physical properties.