The correct answer is D. As the chocolate bar changes from a solid to a liquid the particles move around more.
Step-by-step explanation:
Changes in the state of a substance (for example from solid to liquid) affect the arrangement and motion of the particles. In this way, in the solid-state particles are organized in a fixed structure and only vibrate; however, as the substance is heated and the state of the substance changes (for example, the chocolate bar is melted) particles gain energy, and this makes them move around more, which causes liquids to have an undefined shape. According to this, in the case of a chocolate bar "As the chocolate bar changes from a solid to a liquid, the particles move around more".