The passage mainly explains

why ice is less dense than water and how that shapes winter lakes (The passage connects the open crystal pattern in ice with floating surface ice and liquid habitat below.)

Why is ice less dense than liquid water?

Its molecules form an open pattern that occupies more volume (Freezing arranges water molecules in an open pattern, so the same mass takes up more space.)

Why does water near four degrees Celsius tend to sink below colder water?

It is denser than the colder water (The passage states that water near four degrees is denser, and denser water sinks beneath less dense water.)

In this passage, “volume” means

the amount of space something occupies (The same mass of ice occupies more volume, meaning it takes up more space.)

Why Ice Floats: Level 3 Reading Comprehension Questions

Density describes how much mass fits into a given volume. Many materials become denser as they cool because their particles pack more closely. Water follows that pattern only down to about four degrees Celsius. Below that temperature, its behavior begins to change.

As water freezes, its molecules lock into an open crystal pattern. The pattern holds them farther apart than they were in liquid water. The same mass now occupies more volume, so ice is less dense than liquid water. That difference, not a change in weight, lets a piece of ice float.

The unusual pattern shapes a lake in winter. Water near four degrees is denser than colder water and sinks. Colder water stays nearer the surface, where it can freeze. The floating ice forms a lid that slows heat loss from the water below.

The lid does not make every lake safe or equally warm. Shallow water can freeze deeply, and oxygen may still become scarce. Yet in many lakes, liquid water remains below the ice, giving fish and other organisms a place to survive until spring. A molecular arrangement too small to see helps organize an entire winter habitat.

Comprehension questions