Which event always involves a chemical change? boiling melting conducting burning

The correct answer to the question is burning.

EXPLANATION:

Before answering the question, first we have to understand nature of physical and chemical changes.

A change is said to be physical if there will be no change in chemical configuration of reactants and products. In this process, there will be only change in the physical state of the substances. No new substance is formed in this type of reaction.

A change is said to be chemical if the chemical configuration of the substance is changed . In this type of change, a new compound is formed which have different properties as compared to the reactants.

Out of the four options given in the question, only burning is a chemical change. During burning of a substance, we can not get back the substance which is already burnt .

Boiling, melting and conducting are physical changes. During boiling and melting, there will be state change only.

Hence, the correct answer is burning.

frequency or wavelenth of em radiation in a vacuum