Richard and Brooke's teacher tells them to place 30 marbles in an 8-inch baking pan to make a model. She tells them that each marble represents
a water molecule in the liquid state. Then she asks them to move their
model to show what happens to the liquid water molecules when heat is
added. What do Richard and Brooke do to show this?
They spread the marbles to the edges with their hands.
They tilt the pan so the marbles move to one side of the pan.
They push the marbles to the center of the pan with their hands
They gently shake the pan causing the marbles to move back and forth.

The correct answer is - They gently shake the pan causing the marbles to move back and forth.

Explanation:

When water is heated the molecules present in its liquid state start to move and vibrate faster and allows the water to expand and increase in volume. If the heat is continuously applied to the water its molecules move even faster and escape in the form of molecules of vapor to the atmosphere.

To exhibit this phenomenon by the marble and pan, Richard and Brooke should gently shake the pan causing the marbles to move back and forth which shows faster vibration and movement of molecules.

the answer is definitely c.