Which event always involves a chemical change?

A. Boiling

B. Melting

C. Conducting

D. Burning

Answer

Boiling and burning always involve chemical changes in substances, while melting and conducting are physical changes.

Explanation

Boiling always involves a chemical change. When a substance boils, it undergoes a phase change from a liquid to a gas, and this is typically accompanied by the breaking and forming of chemical bonds.

In contrast, melting is a physical change where a substance transitions from a solid to a liquid state without any chemical reactions occurring.

Conducting refers to the ability of a material to allow the flow of electric current, which doesn't necessarily involve a chemical change.

Burning is another example of a chemical change. During burning, a substance reacts with oxygen to produce new substances, such as ash, gas, and heat.