When compounds form, which of the following statements is true about the elements that form them?

A. their properties do not change.

B. their properties are an average of all elements in the compound.

C. their properties change completely.

D. their properties are completely random.

C. Their properties change completely.

Explanation:

The electron configurations of the elements show a periodic variation with increasing atomic number. Consequently, there are also periodic variations in physical and chemical behavior.

When atoms interact to form a chemical bond, they combine in order to achieve a more stable electron configuration. As a consequence, the compounds formed exhibit completely different properties.

For example, when solid magnesium burns in air, it forms both magnesium oxide and magnesium nitride, which are gases.