The particles gain mass. The particles contain less energy. The particles move more rapidly. The particles increase in volume.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: How are the particles in a block of iron affected when the block is melted?
Possibilities:
- The particles gain mass.
- The particles contain less energy.
- The particles move more rapidly.
- The particles increase in volume.

The particles move more rapidly.