Answer:
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.
