Question

Malik is investigating the properties of helium. Malik finds the chart below about helium in a textbook.



Malik uses models to study helium as different states of matter. He also investigates the motion of helium molecules.

Multiple Choice Question

Malik draws a model to explain changes of state for helium as shown.



Step X describes how helium gas could become a liquid. Which of the following could be the label for Step X?

A. 

Thermal energy is removed and molecular motion increases.

B. 

Thermal energy is added and molecular motion decreases.

C. 

Thermal energy is added and molecular motion increases.

D. 

Thermal energy is removed and molecular motion decreases.

Answer 1

To convert helium gas into a liquid, thermal energy must be removed from the gas, which causes the molecules to move less vigorously and thus come closer together as they transition into the liquid state.

Given this, the correct label for Step X is:

**D. Thermal energy is removed and molecular motion decreases.**