Final answer:
Water is unique due to its polarity, high heat capacity, and ability to form hydrogen bonds, which lead to high boiling and melting points compared to similar-sized molecules. Its cohesive and adhesive properties, along with being a universal solvent, are essential for life and various Earth processes.
Step-by-step explanation:
Water is such a unique molecule due to several distinct properties, largely stemming from its structure and intermolecular interactions.
The polarity of the water molecule contributes to its high heat capacity and heat of vaporization, which are fundamental in regulating Earth's climate and sustaining life.
Furthermore, water's cohesive and adhesive properties, stemming from hydrogen bonding, enable it to climb up plant roots and stems and are crucial for soil moisture retention.
This cohesion and adhesion, along with its ability to dissolve many substances, are why water is known as the universal solvent.