The correct statement is option 4: "The temperature at which a solid changes into a liquid is called the boiling point."

This statement is not correct because the temperature at which a solid changes into a liquid is called the melting point, not the boiling point. The boiling point is the temperature at which a liquid changes into a gas.

Let`s analyze the other options to understand why they are correct or incorrect:

Option 1: "Conduction can occur easily in solids, less easily in liquids but hardly at all in gases." This statement is correct. Conduction is the transfer of heat through direct contact between particles. Solids have tightly packed particles, allowing efficient conduction. Liquids have more loosely packed particles, which slows down conduction. Gases have widely spaced particles, making conduction nearly impossible.

Option 2: "Heat energy is carried by moving particles in a convection current." This statement is correct. Convection is the transfer of heat through the movement of fluid (liquid or gas) particles. When heated, the particles become less dense, rise, and create a convection current. This movement carries the heat energy.

Option 3: "Heat energy is carried by electromagnetic waves in radiation." This statement is correct. Radiation is the transfer