The correct answer is option 4: 4°C.

Water has a unique property where its density decreases as it cools down from 4°C to 0°C. However, as the temperature decreases further and water freezes, the density increases again.

At 4°C, water has the maximum density. This means that at this specific temperature, a given volume of water weighs the most.

Aquatic animals benefit from this property of water because it allows them to thrive in colder environments. As water cools down, it becomes heavier and sinks, creating a circulation pattern in bodies of water. This helps to distribute oxygen, nutrients, and heat to the deeper parts, making it easier for aquatic animals to survive.

It is important to note that this is a unique property of water, as most substances become denser as they cool down and freeze.